Forensic Science Introduction to Forensics PDF

208 Introduction to Forensic Science 7.2.12 Ear and Lip Pattern Evidence (Pinnascopy and Cheiloscopy) 7.3 HAIR ANALYSIS The use of lip marks and ear shape patterns has been proposed as another way of linking a biological feature to a particular...

208 Introduction to Forensic Science 7.2.12 Ear and Lip Pattern Evidence (Pinnascopy and Cheiloscopy) 7.3 HAIR ANALYSIS The use of lip marks and ear shape patterns has been proposed as another way of linking a biological feature to a particular 7.3.1 Introduction person. In order for any technique to be employed, it must first be demonstrated that it provides unique information and that In the early stages of human development, both the skin and the information is permanent (does not change over time or by hair form from the ectoderm (the outermost layer). As such, design). hair and skin not only share a strong biological connection, Lips have been shown to contain many “elevations and as hair is considered a derivative of our skin, but also, more depressions” along their surfaces (sometimes called grooves), simply, both of these tissues are primarily found on the out‑ although these do not have direct biological similarity to the side of the organism. Therefore, hair and skin are the compo‑ ridges found in fingerprints (Figure 7.31). It was proposed as nents of our bodies that directly interact with the environment early as 1902 that the patterns formed by these grooves could and can easily leave lasting and identifiable forensic evidence. provide a means of personal identification. A number of meth‑ Because of the similarity between hair and fibers in their form ods for identifying lip mark features have been developed, and forensic function, we will consider them together in this although none has gained general acceptance. section, beginning with a discussion of hair. A number of studies have been undertaken to determine Hair and fiber samples are among the most durable of all bio‑ whether cheiloscopy, the study of lip groove patterns, meets logical materials and retain much of their forensic value for many the requirements of scientific validity to define legal unique‑ years. While most biological tissues quickly degrade after death, ness, persistence, and permanence. Cheiloscopy has been hair samples have been known to persist virtually unchanged for used in several court proceedings with mixed admissibility even thousands of years. These samples can provide both struc‑ results. One study in Japan measured the lip marks of over tural and chemical clues as to both their individual origin and the 1,300 subjects, including several identical twins, and found underlying biochemistry that formed them. Similarly, durable them uniquely different. Researchers then followed a number fibers, both natural and manmade, found throughout our soci‑ of subjects for several years and noted that the patterns did not ety in cloth and other items, can also provide useful information appear to change. However, the scientific validity of the tech‑ about their origin, composition, form, and use. nique remains unverified, and a great deal of work is needed before this method can find acceptable use in forensic investi‑ gations and courtroom proceedings. 7.3.2 Hair and Fur In a similar fashion, the shapes of people’s ears have shown significant variation and have been used to link a par‑ Hair is a complex appendage that grows from a follicle in the ticular person with a “found” earprint (pinnascopy), such as on skin of mammals only. One of its main purposes is to help reg‑ a window, door, or mirror (Figure 7.32). ulate the body temperature of an organism by either trapping FIGURE 7.31 Typical pattern of grooves found on lips. Source: Used per Creative Commons Attribution 2.0 Generic. User: Tania Saiz.  7 Anatomical Evidence: The Outside Story 209 FIGURE 7.32 Examples of the variety of known ear shapes. Source: Shutterstock.com. or releasing warm air near the skin’s surface. The protective function of hair and its exposure to extreme conditions require it to be physically strong, highly flexible, and chemically durable. Hair exhibits enormous diversity of form, both between different species of organisms and from individual to individ‑ ual. Traditionally, hair that comes from non‑human mammals is referred to as fur rather than hair, but the structures are very similar. 7.3.2.1 Composition of Hair Hair is composed of about 80–90% protein, mostly kera‑ tin and melanin, and between 8% and 15% water, with the remainder mostly as lipids. Keratin is a tough, durable, fibrous protein composed of long chains of amino acids and typically found as a structural component of hair, nails, horns, and claws. Melanin, however, is a pigment polymer derived mostly FIGURE 7.33 Skin and hair follicle anatomy with the apocrine, from the amino acid called tyrosine that imparts the color to sebaceous, and eccrine glands along with other details of hair a hair sample. Generally, the darker the hair coloration, the structure. more melanin it contains. There are, however, several types of melanin commonly found in hair. The dark pigment called Source: Shutterstock.com. eumelanin colors black and brown hair, while the pigment called pheomelanin is the main coloration chemical found in 7.3.2.2 Hair Structure red hair. Blonde hair simply has lower amounts of melanin overall, while gray hair typically lacks melanin completely. Hair grows from a hair follicle, a tiny hole in the skin located All hair samples have very similar chemical compositions, within the outermost layers of the skin, as shown in Figure 7.33, which limits the use of chemical analysis in the individualiza‑ and consists of a root, shaft, and tip. The hair shaft grows from tion of a hair sample as coming from a particular person. the base of the follicle in an area known as the dermal papilla 210 Introduction to Forensic Science several layers as cells die (Figure 7.34). The portion of the hair shaft that extends beyond the surface of the skin is, therefore, composed mostly of dead keratinized (cornified) material. The only living portion of a hair is the portion that is located in the follicle. It is important to note that since the cells in the shaft are dead and keratinized, it is almost never possible to extract nuclear DNA from a hair shaft. Mitochondrial DNA, however, can often be found in the shaft and is stable for long periods of time. It is possible to collect nuclear DNA from a hair sample only if the sample contains some of the living cells from either the hair root or from the follicle itself. This is common if a hair has been forcibly removed and some of the tissue from the fol‑ licle is pulled out with the hair fiber. The follicle has associated with it sebaceous glands that produce sebum, an oily material that protects, lubricates, waterproofs, and helps to inhibit the growth of microor‑ ganisms on the hair. The follicle is also attached to a mus‑ cle (arrector pili muscle) that serves to elevate and lower the hair fiber in response to environmental conditions. Contraction of the erector pili muscles also produces what are commonly known as “goosebumps.” Thus, when it’s cold outside, the erector muscles contract to raise the hair shaft, trapping a layer of warm air next to the skin to help keep us warm and conserve body heat. Each mature hair fiber is typically made up of three components: the cuticle, cortex, and the medulla. The outermost translucent layer of a hair shaft is called the cuticle, which appears similar to the shingles on a roof or the outer scales of a snake’s skin, with the exposed portion of the “scale” aimed toward the tip of the shaft (Figures 7.36 and 7.37). You can sometimes feel this directionality of the cuticle scales by first running your pinched fingers along a hair shaft from your head toward the end of the hair and compar‑ ing it with running your fingers in the opposite direction from the tip. It often feels rougher when moving from the tip toward the scalp since this is moving against the “grain” of the cuticle scales toward your head. This relatively thin layer, usually just six to ten cells thick, protects the hair by forming a waterproof and rather chemically resistant layer that coats and protects the entire shaft. The pattern formed by the overlapping cuticle cells is very distinctive and can be easily used to determine the spe‑ cies of animal that produced the hairs (Figure 7.37). The three FIGURE 7.34 (Left) Hair shaft structure and (Right) scanning general types of scale patterns most commonly observed, electron micrograph (SEM) of hair shafts growing from the sur- shown in Figure 7.36, are the coronal (“crown‑like”), spinous face of human skin. (“petal‑like”), and imbricate (“shingle‑like”) patterns. The coronal pattern, common in small rodents, appears similar to Source: Left, Shutterstock.com. Right, Steve Gschmeissner/ an arrangement of stacked “crowns” or circular bands. The spi‑ Science Photo Library. Used with Permission. nous pattern, found in the hairs of cats and mink, appears like triangular “petals” that often project away from the shaft of to form a rapidly elongating hair bulb. The growing hair root the hair. The imbricate pattern, found in human hair, appears is fed by its own blood supply with new cells pushing the pre‑ as flattened scales. viously formed cells upward. When the hair shaft grows, the Since the cuticle is the part of the hair directly exposed follicle deepens into the skin layers while the shaft grows out to the environment, it is susceptible to damage by sunlight, of the follicle. As the shaft elongates, the hair begins to form wear, and the way that people treat and style their hair.  7 Anatomical Evidence: The Outside Story 211 BOX 7.6 COPERNICAN HAIR? Nicolaus Copernicus (1473–1543) was a Renaissance church canon and astronomer who forever changed our perception of the Universe and our place in it. Prior to his work, the prevailing attitude was that the Earth was the center of the Universe and everything else revolved around it. Copernicus, however, argued that the sun was instead the center and that the earth and all planets moved around it. Historians often point to his seminal work as the beginning of the scientific revolution and modern science. But until recently, the remains of this influential scientist were missing. When he was buried in Frombork Cathedral, Poland on May 24, 1543, beneath the altar floor, the place of his intern‑ ment was not marked and ultimately lost to history (Figure 7.35a and b). In 2005, however, a skull and some remains were unearthed, after an intensive five‑year search of the Cathedral, which archaeologists thought might be those of Copernicus. Scientists were able to extract some mtDNA from one of the teeth in the skull and a femur bone, but the problem was what to compare it with? As it turns out, key evidence came from an unlikely place. In the Stoefler Almanach Copernicus library in Uppsala, Sweden, two hairs were amazingly found in a 16th‑century astronomy reference book that had definitely belonged to the great astronomer. Mitochondrial DNA extracted from the hair samples was found to match well with the mtDNA extracted from the bone fragments, providing very strong evidence that the skeletal remains found in the cathedral were those of Copernicus. Using facial reconstruction techniques on the skull, scientists created a reconstruction of Copernicus’ face that cor‑ responds remarkably well with existing portraits of the astronomer. On May 25, 2010, his remains were reburied with full honors beneath the altar where they were found. FIGURE 7.35 (a) Astronomer Nicolaus Copernicus, from the painting entitled Conversations with God made in 1873 by Jan Matejko (in the background is Frombork Cathedral where he is buried), and (b) Nicolaus Copernicus’ famous treatise, entitled De revolutionibus orbium coelestium (translated as “On the Revolutions of the Heavenly Spheres”), published in Nuremberg in 1543 and was the first to offer an alternative explanation of the workings of the Universe with the sun as the center of rotation. Source: Right, Used per Creative Commons Attribution‑Share Alike 4.0 International license. User: Sam.Donvil. For example, dyeing, drying, and styling hair can permanently one another (Figure 7.38). When stretched, these molecules damage this layer. can uncoil like a spring, and when released, the molecule can If we could peel back the outer cuticle layer, as shown in reform its original coiled structure, giving hair its observed Figure 7.38, the underlying cortex layer would be exposed. The elasticity. Pigment molecules, giving hair its color, are also cortex makes up most of the bulk of the hair shaft and gives largely found in the cortex layer. the hair its characteristic elasticity, stretching up to 30% of its Occasionally, small structures are observed within the length without breaking. The cortex is primarily made up of cortex of a hair fiber, providing additional comparative infor‑ long, twisted, and coiled protein fibers, like a spiral staircase, mation. For example, air bubbles (known as cortical fusci), that easily bend and stretch when the long molecules slide past pigment bodies (small areas of pigment concentration), and 212 Introduction to Forensic Science FIGURE 7.36 (On Left, Top to Bottom) Cuticle hair patterns: coronal, spinous, and imbricate, and (Right, Top to Bottom) (a) coronal scales of Free‑Tailed Bat Hair (Tadarida brasiliensis), (b) spinous proximal scales of mink (Neovison vison), and (c) imbricate distal scales of mink (Neovison vison). Source: FBI. FIGURE 7.37 Cuticle patterns for several animal species; (Clockwise from Upper Left) a. human hair (Homo sapiens), b. dog hair (Canis lupus familiaris), c. reindeer hair (Rangifer tarandus), and d. camel hair (Camelus dromedarius). Source: All images Source: Power and Syred/ Photo Library images. Used with permission. ovoid bodies (larger pigment‑containing structures with The ratio of the diameter of the shaft to the diameter of ­regular boundaries) are observed. Ovoid bodies, often found the medulla can be defined as the medullary index (MI), which in dog hair but only occasionally in human hairs, are shown can be used to help distinguish human hair from that of other in Figure 7.39. animals. In many animals, the MI is greater than 0.5, while in The third and innermost component of hair is the medulla. humans it is typically found to be less than 0.3. This part of the hair is characterized by either very spongy Hair varies greatly depending on its location on the body. cells or no cells at all, forming a canal‑like structure in the As a fetus, our entire body is covered with very fine color‑ center of the shaft, often called the medullary canal. Melanin less hair, called Lanugo. During early childhood, however, this can sometimes be found in this layer, contributing to the color lanugo hair is lost, and the majority of our body is covered of the hair. The medulla in human hair can form a continuous with fine short hairs, called Vellus hair or sometimes referred canal, be interrupted by areas without a medulla, or be miss‑ to as “peach fuzz”. During puberty, humans develop longer, ing altogether (Figure 7.40). The medulla pattern for some ani‑ thicker, colored hair on various parts of the body, besides the mals can be rather complex showing ladder‑like or lattice‑like scalp and eyebrows, called terminal hair, which forms part of patterns. our secondary sex characteristics. Terminal hair includes hair  7 Anatomical Evidence: The Outside Story 213 FIGURE 7.38 Scanning electron micrograph (500x) showing a human hair with the cuticle folded back to reveal the underlying cortex layer. Source: Natural History Museum, London/Science Photo Library. Used with permission. FIGURE 7.39 Photomicrograph of Ovoid Bodies: the presence, abundance, and distribution of these pigment‑dense regions can be useful points of comparison. Source: FBI. found on our scalps, in armpits, on legs, as chest hair, and in type of hair. For example, until puberty, the facial follicles on the pubic area. a male produce only fine vellus hair. During puberty, these Usually, a single hair follicle produces only one type of follicles change to produce a characteristic male beard made hair, but sometimes a follicle can change to produce a different up of thicker, longer terminal hair. Similarly, follicles on the 214 Introduction to Forensic Science medulla, while pubic hairs are typically short, with a tapered Missing or rounded tip, and contain a relatively broad medulla. Because of the variation of hair structures, even on one individual per‑ Continuous son, it is often necessary to collect many hair samples in order to get a representative sample. This variation in a single indi‑ Fragmented vidual makes it very difficult to determine if a particular hair fiber originated from a particular person. Ladder 7.3.2.3 How Hair Grows Multiserial Ladder Hair growth occurs in a cycle composed of three main stages: the anagen, catagen, and telogen phases (Figure 7.41). The FIGURE 7.40 Patterns observed in hair medulla. lengths of these cycles are genetically programmed and can vary greatly from person to person and from place to place on the body. For example, an entire cycle can take four to five scalp usually produce only terminal hair, but in some instances years for scalp hair, while the cycle is completed in three to (e.g., androgenetic alopecia), the follicle can change to produce four months for eyebrow hair. In humans, these stages do not short, thin, lightly colored hair. occur at the same time for all the follicles – each follicle has Most animal hairs are divided into three basic types: guard its own timetable. This, however, is not true for other animals hairs (from the outer coat for protection), fur (from the inner in which the phases may be timed to occur simultaneously coat for insulation and temperature regulation), and tactile accompanied by the shedding of hair, for example, when a rab‑ hairs (for sensing, such as whiskers). Human hair, however, is bit changes its hair from the darker summer coat to the white not so well‑differentiated, resembling animal fur most closely. winter coat of hair (Figure 7.42). The overall shape and length of a human hair can give The anagen phase is the part of the cycle in which information about where on the body it originated, such as the active growth occurs. During this phase, the cells at the base scalp, face, pubic area, or elsewhere. For example, scalp hair of the follicle rapidly divide and push “upward” to produce is usually long with cut or split tips and a relatively narrow the new hair shaft. The cells in the base of the growing hair FIGURE 7.41 Hair growth phases: anagen is the growth phase, catagen is the transitional phase, and telogen is the resting or ­quiescent phase. Source: Shutterstock.com.  7 Anatomical Evidence: The Outside Story 215 FIGURE 7.42 Winter (L) and summer (R) coats of a snowshoe rabbit (Lepus americanus) as an example of correlated hair growth phases. Source: Images used courtesy Shutterstock.com. FIGURE 7.43 Naturally shed hair fiber showing the characteristic “club” end shape. Source: FBI. bulb are the second fastest‑growing cells in the body (after by about two‑thirds through cell death and detaches from the the b­ lood‑­producing cells of the bone marrow). In humans, root, forming a “club”‑shaped end (Figure 7.43). This process this phase can last between several months and many years, results in major destruction of the lower part of the hair fol‑ depending on where the hair is growing. licle, including the cells that produce the keratin and melanin Generally, a hair fiber grows about ½ in. (~1 cm) per that form the hair. Usually, the catagenic phase lasts several month (0.3–0.4 mm/day). Thus, the tip of an individual hair weeks for all types of hair. that is a foot long began growing within the follicle about two The final phase, the telogen phase, is a resting period for years earlier. the follicle. In this phase, the detached club root has com‑ The catagen phase can best be thought of as a transitional pletely formed. The bulb on the dead hair helps to keep the phase and usually represents about 3–5% of all body hairs at hair in the follicle tube but the hair eventually falls out since any given time. It is during catagen that hair growth stops, and it’s no longer strongly “connected” to the follicle. This phase the portion of the follicle surrounding the hair root shrinks can last from a few months to years, depending on its location 216 Introduction to Forensic Science on the body and usually about 10–15% of all hairs are in the telogen phase at any given time. On average, a typical per‑ son has between 100,000 and 150,000 hairs on their head and loses between 50 and 100 hairs every day due to the normal hair growth cycle. A fourth phase, the exogen phase, is sometimes consid‑ ered, although it is associated with the hair fiber itself rather than with the follicle and simply has to do with the loss of the hair shaft from the follicle. This process is poorly understood, however, but it is believed to be important in the timing of the restart of a new anagen phase of hair growth for the follicle. These phases typically continue over the entire lifespan of a person. Sometimes, however, this pattern is either inter‑ rupted or the follicle is destroyed by medications, radiation, genetics, accidents, or other causes. BOX 7.7 CAN YOUR HAIR TURN WHITE OVERNIGHT WITH FRIGHT? There are plenty of stories throughout history where someone, faced with extreme fear or a severely traumatic FIGURE 7.44 Ethnic differences in hair structures in cross‑­ experience, reportedly has their hair turn completely section: (Top) Caucasian, (Middle) African, and (Bottom) Asian. white overnight. Legend has it that the hair of some Source: FBI. famous people, such as Sir Thomas More (1535), Henry of Navarre, later Henry IV of France (1572), and Marie Antoinette (1793), went white overnight when faced with 7.3.2.4 Sex and Ancestry Differences imminent death. These tales, however, do not have a basis in current in Hair Structure scientific research. White hair arises from fibers that Occasionally, ancestry differences can be seen in hair sam‑ do not contain any melanin pigments. When someone ples (Note: race does not provide an accurate representation goes “gray”, it simply means that they have a mixture of of human biological variation). This will be described in more colored and uncolored (white) hair. Since the amount of detail in the chapter on forensic anthropology, but occasion‑ pigment in a hair fiber is fixed at the time it forms within ally, some information regarding ethnicity may be gained by the follicle, even if a hair follicle stopped producing mel‑ examining hair samples, as shown in Figure 7.44. anin overnight, the hair fiber beyond the follicle would Hair of Asian ancestry tends to be round in cross‑section still remain pigmented since the hair is dead. Thus, if all with a greater diameter than other types, although generally less the follicles on a person’s head stopped producing mela‑ dense than hair of other ethnicities. This tends to lead to hair nin at once, the hair would still be largely pigmented. that is thicker, straighter, and more difficult to curl than hair of Additionally, there is no research evidence that shows other origins. Caucasian hair tends to be oval in cross‑section that stress can significantly cause hair to stop producing and more physically durable to bending and stretching than melanin or go white; it’s largely determined by a per‑ hair of other ancestral types. It is also often relatively straight son’s genetics, age, or access to bleach. but flexible so as to form loose curls easily. African hair tends to There is, however, a fairly rare autoimmune dis‑ be oval to relatively flat (“ribbon‑like”) in cross‑section, allow‑ ease (a disease in which your body’s immune system ing it to form tight curls readily while remaining very strong turns against itself) called alopecia areata in which across the width of the fiber. Additionally, the fiber tends to hair ­follicles are very rapidly destroyed, even over a few vary greatly in its thickness and twists along the length of the days. There is a particularly rare form of this disease, shaft in contrast to other ethnicities. however, that seems to attack only the pigmented hair It is typically very difficult to determine the age or sex follicles, leaving a person with only unpigmented or of an individual from hair samples. It is sometimes possible, white hair. Assuming that all the pigmented hair fell out although rarely done, to recover follicle cells from the root ­immediately, the remaining white hair would remain, of forcibly removed hairs. These cells can be stained and giving the appearance of a rapid transformation from examined under the microscope to reveal specific sex‑related colored or gray hair to white hair – but this certainly ­characteristics, such as the Barr body for females or a Y body would not happen overnight. for males.  7 Anatomical Evidence: The Outside Story 217 7.3.2.5 Hair Treatment used to chemically open up the cuticle, thereby allowing the dye to penetrate into the cortex, and to catalyze coloration Hair has important cultural significance beyond its necessary reactions in the cortex. This process also breaks the majority biological functions. People style, condition, shampoo, color, of the sulfur‑sulfur bonds holding the inner keratin strands of cut, and modify their hair in innumerable ways. Today, over the hair together, releasing the characteristic odor of hydrogen 50% of people in the United States report that they color their sulfide and causing the hair to “relax”. The hydrogen peroxide hair, with red being the most popular choice. Each process we is used to remove the pre‑existing natural color of the hair do to our hair can be “recorded” in the fibers, and this record and facilitate the reformation of the sulfur‑sulfur linkages. can help to individualize a fiber by marking the history of Finally, a conditioner is used to try to close the scale‑like its treatment. These modifications can, therefore, be used to structure of the cuticle after the process is completed. Often, advantage to help identify a particular hair and to learn some‑ however, this harsh chemical process results in a damaged thing about its past. cuticle layer that can be helpful in forensic investigations by The color of hair can be readily altered through the use of telling a story about any recent treatment of the hair, as seen dyes and rinses. To permanently change the color of hair, how‑ in Figure 7.45. ever, pigment molecules must pass through the outer cuticle It is occasionally possible to determine a rough timeline layer and be deposited within the cortex. When pigment mol‑ of when the dyeing process may have occurred by observing ecules adsorb only on the outer cuticle layer, the color may be cuticle damage that is found some distance along the fiber but vibrant, but it is also readily removed by simple washing. This not at the base of the shaft (the youngest part of hair). By not‑ is the case with temporary coloration methods such as certain ing the distance from the base of the fiber to the beginning of rinses, sprays, and foams. the damaged area, a rough indication of how long ago the dye‑ For a more permanent coloration, the pigment molecules ing process occurred can be estimated given the average rate must first penetrate the tough outer cuticle. This requires a of growth of the hair and knowing that hair grows only from modification of the cuticle to make it permeable to the pig‑ its root. Additionally, observing a sharp color change near the ments since its primary function is to protect the cortex from root end of the hair fiber, with color that is dense and relatively the environment, and it, therefore, resists the movement of even throughout the cortex, is evidence that the hair has been pigment into the hair. In order for permanent coloration to dyed. occur, the cuticle must be chemically treated to open up its Hair can also be modified by curling, waving, or straight‑ scale‑like structure, requiring relatively harsh chemical pro‑ ening through a process often called permanent curling or cessing. This usually employs an oxidizing agent, an alkaline “perming.” About one‑quarter of the keratin in hair, the major (basic) agent, and a conditioner in addition to the dye. An oxi‑ protein component that gives hair its characteristic shape, is dizing agent is something that removes electrons from a mol‑ composed of cysteine, a sulfur‑containing amino acid. The ecule, such as hydrogen peroxide (H2O2). An alkaline agent is keratin chains in hair are linked together by connecting the a basic chemical, such as ammonia (NH3), that can react with sulfur atoms on two adjacent chains, forming disulfide bonds. acids. In the permanent dyeing process, ammonia is often These linkages largely fix the shape of the strand in much the FIGURE 7.45 Micrographs of damaged cuticles from the hair treatment processes. Source: Nobeastsofierce/Science Photo Library image. Used with permission. 218 Introduction to Forensic Science Broken S-S Reformed but bonds mismatched Keratin chains S-S bonds FIGURE 7.46 Disulfide bond breakage and “mismatched” reformation during the “perming” process to hair to create a permanent curl. same way that the rungs of a ladder hold the two vertical poles sample sufficiently to connect it with one individual person. together to give rigidity and structure to the ladder, as shown Therefore, scientists try to find ways that do individualize a in Figure 7.46. When hair is chemically “permed,” a chemical hair sample. One way is to identify the hair as associated with (such as sodium thioglycolate) is first used to break about 30% a ­disease, abnormality, treatment, or infestation. For example, of the disulfide bonds between the keratin strands. As the hair a ­deficiency of certain vitamins or minerals, such as a zinc defi‑ is placed in the desired shape, the keratin strands are now free ciency, can result in abnormal hair growth that can be detected to slide past each other to assume the new shape. Then, another in the hair. If a suspect suffers from a similar deficiency, a chemical, such as hydrogen peroxide or a similar oxidizing better link can be made between the recovered sample and a agent, is applied to reform the disulfide linkages between adja‑ hair sample of known origin. Abnormalities in metabolism, cent cysteine units. In this final step, however, there is now hormone levels, or other biochemical irregularities can also be a new pattern of pairing between adjacent cysteines, thereby detected in hair samples (see Section 7.2.3.7). permanently locking the keratin strands into the new shape. Abnormalities in hair structure can also help in charac‑ This would be something like “unzipping” the rungs of a lad‑ terizing a hair sample. One example of many is the striking der, moving the two poles to a new orientation relative to each pili annulati hair abnormality which arises from an unusual other, and then “re‑zipping” the rungs together to “fix” the new process in forming the keratin of the hair fiber. This condition arrangement of the poles. The curl is permanent only on the results in a cortex that is not solid but rather contains air pockets portion of hair existing when the permanent was done, and as in a regular pattern along the length of the fiber. These air pock‑ new hair grows or the old hair is cut, the effect of the perma‑ ets effectively reflect light so that the hair appears to be banded nent gradually disappears. (Figure 7.48). This distinctive condition is genetic in some cir‑ People also commonly clean and style their hair through cumstances while the cause is unknown in other instances. regular cleaning and the application of hair products. Several Occasionally, it is possible to detect hair infestations, forensically interesting pieces of information can be gained by such as mites (arachnids – related to spiders, not insects), lice considering the types of cleaning and styling chemicals used (insects), and others, as illustrated in Figure 7.49. These can on the hair fibers. Information about any recent washing can help provide both a connection with a known person and infor‑ be revealed microscopically. Additionally, chemical analysis mation about the history of the sample. of the surface or rinsing of the fiber can also show residues of particular types of treatments (see Chapter 12). 7.3.2.7 Hair Toxicology Cutting hair, either to maintain a desired hairstyle or through accident, injury, or assault, can provide information When hair grows within a follicle, certain biochemical condi‑ on the history of a hair sample. Examples of this type of infor‑ tions existing in a body can be chemically recorded directly mation from hair fibers can be seen in Figure 7.47. within a growing hair shaft. Chemicals can be transferred from a person’s bloodstream to the follicle and then depos‑ ited in the growing hair. As the shaft continues to grow, the 7.3.2.6 Diseases Involving Hair chemical record contained in the living portion of the hair is Since everyone’s basic hair chemistry is about the same, pushed out of the follicle and becomes a permanent snapshot it is difficult to individualize chemically a particular hair of what was going on in a person’s biochemistry at the time  7 Anatomical Evidence: The Outside Story 219 FIGURE 7.47 Hair patterns from treatment or injury: (a) hair root naturally fallen out, (b) hair cut by razor, (c) naturally knotted hair, (d) split ends, (e) hair with dandruff, and (f) post‑mortem root band. Source: (a) istockphoto.com, Jan‑Otto, (b, c, d, and e) Shutterstock.com, (f) FBI. FIGURE 7.48 Photomicrographs of Pili Annulati (banded hair). FIGURE 7.49 (Left) Follicle mites (Demodex folliculorum) Source: FBI. emerging from a hair follicle and (Right) lice (Pediculus humanus) case attached to a hair fiber. that portion of the fiber was formed. Once the newly formed Source: Left, Used per Creative Commons Attribution portion of the hair shaft leaves the follicle and dies, this record 4.0 International, Attribution: © Palopoli et al.; licensee can last for a very long time. For example, certain drugs or BioMed Central. 2014. Right, FBI. 220 Introduction to Forensic Science FIGURE 7.50 Structure of ethyl glucuronide (EtG) and ethyl sulfate (EtS). their metabolites (chemicals that the body transforms the drug (EtG), and ethylsulfate (EtS) (Figure 7.50). While alcohol is into), such as cocaine, heroin, amphetamines, and others, are not deposited in hair, these three metabolites of alcohol (etha‑ deposited from a person’s bloodstream to the growing hair nol) are permanently deposited in growing hair fibers, making fiber, providing a long‑lasting record of drug use. a lasting record of its use – even for years. Some drugs, particularly those that are bases, bind tightly There are a number of both important advantages and to the melanin since melanin is acidic. Therefore, the darker challenges when considering toxicology information from the hair, generally the more melanin and the more drug ­binding hair samples. Hair is usually a readily available, non‑invasive, found. Neutrally charged drugs tend to enter the hair more eas‑ inexpensive, and long‑lasting medium for analysis. In addi‑ ily. Some drugs get into the hair through the sebum (sweat), tion, chemical analyses have been developed for trace levels of especially when the cuticle is damaged. Of concern, however, compounds found within hair fibers. But hair analysis also has is that chemicals from the surrounding environment (e.g., dirt, some significant difficulties. For example, darker and coarser smoke, etc.) can also make their way into the hair and affect hair fibers retain drug information longer than lighter and finer any later chemical analysis to detect drugs. hair. This may lead to a different drug use profile determined Since hair grows at a rate of about ½ in. (~1 cm) per month, from hair for two people with identical usages. False positives a rough timeline of drug or poison intake event(s) can be esti‑ may also present significant problems, such as in the determi‑ mated by chemically analyzing different portions of the hair nation of alcohol abuse through EtG analysis. For example, in along the length of its shaft. This form of analysis has become one study, it was surprisingly shown that a false positive can an important part of drug surveillance programs for people on come from a person using an alcohol‑containing hand sani‑ parole, checking to see if a patient has been complying with tizer before the analysis. There are also problems in establish‑ therapeutic drug therapy, or verifying the reliability of a per‑ ing a relationship between the amount of a drug found in a son’s statement regarding their drug use. Besides serving as hair sample with how much was in a person’s blood system. a record of drug use, this toxicological information can also Other problems currently being addressed include: (1) use of aid in determining if two fibers have a common source, for hair from different places on the body, (2) ethnic differences example, one found at a crime scene and one taken from a sus‑ in drug absorption and retention in hair, and (3) the effects pect. Hair can also serve as strong evidence showing a p­ erson’s of cosmetics on chemical composition. Nonetheless, the use long‑term use of alcohol. When alcohol is consumed, the body of hair analysis for drug and toxin exposure is increasing and produces fatty acid ethyl esters (FAEE), ethyl glucuronide forms an important forensic tool. BOX 7.8 THE END OF AN EMPEROR: TELLTALE HAIR? Napoleon Bonaparte (1769–1821) is one of the most studied, despised, and revered figures in history, with tens of thousands of books published on his life and exploits, and thousands of new titles appearing every year. He is certainly a person of intrigue and mystery, but one of the greatest mysteries regarding this enigmatic figure is the cause and manner of his death. After Napoleon lost the Battle of Waterloo in 1815 and later surrendered to the British, he was exiled to the remote tropical island of St. Helena in the South Atlantic, still one of the most isolated places on Earth. He and his retinue of about 20 friends and associates lived for six years on the island under the close watch of the British commander until his death in 1821. Upon his death, an autopsy was performed by British surgeons and the cause was determined to be a perforated (“bleeding”) stomach ulcer that had become cancerous. But today, nearly 200 years later, controversy still remains sur‑ rounding his death. During his exile, Napoleon often thought of escaping and his relations with the British commander on St. Helena, Sir Hudson Lowe, were very poor, indeed. Lowe deeply distrusted Napoleon and had sentries posted constantly to monitor Napoleon’s every movement. Napoleon, in turn, ultimately retreated to his home and grounds, Longwood House, and did everything possible to remain out of the sight of his guards – he even had sunken walkways dug on the grounds to enable him to walk outside without being seen by the sentries.  7 Anatomical Evidence: The Outside Story 221 FIGURE 7.51 (Left) Painting of the death of Napoleon (Charles Steuben) and (Right) Paris Green, an arsenic-containing pigment. Source: Right, Used per Creative Commons Attribution-Share Alike 3.0 Unported. User: Chris Goulet at English Wikipedia. During his exile, Napoleon often wrote and said that he was being “murdered by the British Oligarchy.” His relatively rapid decline, along with the type of illness and symptoms he reported, has prompted speculation ever since that he was murdered, and theories have abounded about how, who, and why he was murdered. But new insights have come from, of all places, locks of Napoleon’s hair. One theory of his death is that he was poisoned by arsenic – a well‑known 19th‑century poison. It was noticed that some of the symptoms of Napoleon’s demise closely resembled arsenic poisoning (Figure 7.51). But how to prove this since Napoleon’s body, removed from St. Helena in 1841 to a crypt in Paris, is not available for tissue analysis to look for arsenic? As it turns out, something almost as good is available – Napoleon’s hair. As part of an old custom, Napoleon bequeathed locks of his hair to his friends and family upon his death. Since hair provides a long‑lasting record of toxins in the body, analysis of his hair sample should show high levels of arsenic if this was indeed the cause of his death. A bona fide Bonaparte hair sample was ultimately found, and an arsenic analysis was performed. The analysis showed that there were indeed significantly higher levels, nearly 100 times normal, than normal arsenic levels in the former Emperor’s hair. But was he poisoned? Some say yes, while other theories have been proposed to account for the arsenic levels. In 1980, Dr. David Jones proposed that Napoleon was actually suffering from Gosio’s disease, a chronic arsenic poisoning from exposure to a common 19th‑century pigment – Scheele’s or Paris green. Scheele’s green contains copper arsenite that, under certain circumstances of high humidity and mold, gives off arsine gas (AsH3). Almost miraculously, Dr. Jones found what is believed to be an actual piece of Napoleon’s wallpaper from Longwood House that clearly had Paris green pigment (note the painting of Napoleon’s deathbed in Figure 7.51 that shows the green star pattern on the walls). A chemical analysis of this wallpaper pigment showed that it definitely contained arsenic. But was it the cause of death? And why was Napoleon the only one affected? As it turns out, others in Napoleon’s party complained of illnesses and the “bad air” at Longwood, including the butler who also died. But for a normally healthy person, the level of arsenic might not have been enough to cause severe illness. But to someone already in a compromised health state, such as Napoleon with a problematic ulcer, the added effect of the arsenic might have been enough to significantly contribute to his cause of death (proximate cause of death, Chapter 8). Interestingly, when they exhumed Napoleon’s body nearly 20 years later, it had not decayed and was perfectly preserved, even in the warm tropical environment – further suggestioning the presence of arsenic. So, what caused Napoleon’s death? At this point, the evidence is not fully conclusive. and we await more information while the debate continues. What do you think? 7.3.2.8 Hair Comparison and Identification be individualized through its chemical composition or usually even from its structural features. The shaft of a mature human Probably the most important aspect of examining a hair sam‑ hair does not contain nuclear DNA so that only mitochondrial ple is the observed microscopic structure of the medulla and DNA analysis is possible for such samples. Often, however, cuticle of the sample. An individual hair fiber, however, cannot tissue from the follicle may remain at the root of a hair sample, 222 Introduction to Forensic Science such as fibers forcibly removed from the scalp, allowing for the most sensitive portions of our bodies, through which we sense a nuclear DNA analysis. Apart from DNA analyses signifi‑ a great deal of information regarding the shape of the world. cant error rates are associated with the microscopic compari‑ son of two hair samples. When comparing these samples, the color, length, and diameter of the hair fiber are particularly 7.3.3.1 Fingernail Growth important. Like hair, the majority of nails are dead keratinized material. The only living portion is the nail root, or germinal matrix, that extends under the skin opposite to the end of the nail and 7.3.3 Fingernails is where the nerve, blood supply, and lymph vessels are found (Figure 7.52). The nail grows continuously from the root as Fingernails and toenails, like hair, are considered appendages long as it is healthy and nourished, growing an average of 0.5– of the skin and are closely chemically related to the claws, 1.2 mm/week. Fingernails actually grow much faster than toe‑ hooves, and horns found in other animals. Like hair, nails are nails, typically taking about six months to completely regrow made up of the durable protein keratin. The importance of a new fingernail while it may take up to two years to fully nails in forensic cases usually arises in assault or other violent regrow a toenail. cases in which pieces of an attacker’s or victim’s fingernail As new nail cells are produced, they are pushed out of the become lodged in clothing or skin. Finding and analyzing the root area as white, opaque round cells. These newly formed nail can be valuable evidence. cells are visible near the root of the nail as a crescent shape, Nails primarily serve to protect the very sensitive ends of called the lunula (“small moon”). The lunula appears largest our fingers and toes. The tips of our fingers and toes are among on the thumb and gets smaller toward the little finger, where FIGURE 7.52 Finger and fingernail anatomy and structures. Source: Shutterstock.com.  7 Anatomical Evidence: The Outside Story 223 it is often not visible at all. As the cells are pushed further away from the root area, they are flattened, compacted, and Chapter 12 on chemical analysis) was done on these ultimately die, turning translucent, such that the pink blood samples, and high levels of arsenic were found. The capillary bed lying beneath the nail becomes visible. The nail problem was, however, that the surrounding soil in plate, the actual nail itself, rides on the nail bed as it is pushed Greenland was also found to be high in arsenic. But away from the root. At the sides of the nail is the cuticle, or quite importantly, it was found that Hall’s nails and hair eponychium, formed from the flap of skin that folds over the showed that he had received a large dose of arsenic about nail and forms a waterproof seal with the nail. two weeks before his death and that arsenic levels were The shape and structure of nails can tell us about a per‑ low elsewhere in the samples. This differential location son’s health. Nails that are discolored, spotted, brittle, or of the arsenic in the nails strongly suggests that he was grooved may indicate an underlying disease process before poisoned. If the arsenic had come from the Greenland other symptoms appear. For example, pitting may indicate soil, a uniform distribution of arsenic in the entire sam‑ psoriasis, white nails may suggest hepatic failure (liver), or a ple would be expected rather than what was found. blue coloration may suggest circulatory problems. Given the high arsenic levels in Hall’s nails in some places and not others, coupled with the symptoms that he reported before his death, it suggests that homicide should BOX 7.9 A VERY COLD CASE: be the true manner of his death. There remains, however, AN ARCTIC MYSTERY little evidence to tie one particular person with this crime. In 1871, Captain Charles Hall led a congressionally backed expedition on the ship Polaris in search of the North Pole (Figure 7.53). When the expedition came within 7.3.3.2 Forensic Nails Use 500 miles of the pole in late fall, Captain Hall decided Fingernails can be used forensically in a number of ways. In to set anchor and winter aboard the Polaris, much to the one case, a broken fingernail was found in the clothing of a distress and outrage of several crew members. One day suspect. This fingernail was matched with a broken fingernail in late October, after drinking a cup of coffee at anchor, on the victim, both in lengthwise striations and in the irregular Captain Hall became quite ill and thought he had been tearing of the broken nail from the victim’s nail plate. Work poisoned. He died in early November before help could be has also shown that the striations in fingernails do not change arranged. He was buried in Greenland, and a later medi‑ over a person’s lifetime (persistence) and are similar to a cal examination found that he had died of natural causes. unique “barcode” for a person’s nails (Figure 7.54). The case rested here until 1968 when Hall’s body Fingernails are often found with tissue fragments attached was located, exhumed, and an autopsy performed onsite. to them when they have been forcibly removed. The attached Hair and fingernail samples were also taken for later tissues can yield viable DNA samples. This technique has been chemical analysis. A neutron activation analysis (see successfully used in many cases, and the resulting evidence has led to numerous convictions. Additionally, like hair, fin‑ gernails can “record” biochemical information as they grow. There are reported cases that use the analysis of nails to show the non‑uniform presence of toxins, such as arsenic, along the length of the nail, suggesting that the toxin was administered at specific times to the victim. BOX 7.10 DO FINGERNAILS CONTINUE TO GROW AFTER DEATH? Many people believe that fingernails continue to grow after death and exhumed bodies appear to have much longer nails than expected. It turns out this is actually an illusion based on our normal “living” expectations. The growth of the nails does indeed stop at death. However, after death, the tissue surrounding the nails shrinks and dehydrates, making it appear that the fin‑ gernails are longer. Since we are used to seeing finger‑ nails grow and fingers remain the same size in life, we interpret what we see after death similarly – we assume that the finger tissue has remained the same size when it FIGURE 7.53 Capt. Charles Hall (1821–1871). actually shrinks. 224 Introduction to Forensic Science SEM of a fingernail collected over five years (Courtesy of Dr. H. MacDonell). FIGURE 7.54 SEM micrographs showing that fingernail striations remain unchanged over five years. Source: Used and with permission Herb McDonald. 7.4 FIBER ANALYSIS A C 7.4.1 Introduction B D While manmade and natural fibers, other than hair and fur, are not formally biological materials derived from skin, they are often quite similar in their overall structure and function FIGURE 7.55 Natural, regenerated, and synthetic fibers: (a) cotton to hair. Fibers, however, are frequently woven together into fibers, (b) wool fibers, (c) nylon fibers, and (d) polyurethane fibers. cloth and other objects to form both insulating and protec‑ tive layers that lie adjacent to our skin, enhancing the capa‑ Sources: (a) Used per Creative Commons Attribution bilities of our skin in some respect. But our uses for fibers 3.0 Unported, User: Featheredtar, (b) Used per Creative Commons Attribution‑Share Alike 3.0 Unported, User: go well beyond our needs simply for cloth. Fibers are twisted Gerry Danilatos, (c) Used per Creative Commons Attribution into ropes, embedded within other materials to form compos‑ 2.0 Generic, User: Picturepest, and (d) Used per Creative ites, pressed into sheets of hardboard, paper, or felt, spun into Commons Attribution‑Share Alike 4.0 International, User: building materials, and employed in biomedical applications Photon 400 750. from surgical dressings to artificial skin. Because we use fibers for so many everyday functions, they often find their way into forensic investigations and are employed as evidence similarly 7.4.3 Natural Fibers to the way that hair evidence is typically considered. For these reasons, fibers will be considered in this chapter along with Natural fibers are very common and were the first type of skin and hair analysis. fibers to be extensively used by humans to make objects for skin protection and insulation. Wool and dyed flax fibers that were used by early people have been found that date back over 35,000 years. These natural fibers come from many differ‑ 7.4.2 What Are Fibers? ent sources including plants, such as cotton in cloth, wood in paper, and hemp in rope; from insects, such as in silk; from Fibers can be defined simply as long, thin filaments with lengths animals (besides hair and fur), such as catgut and spider’s silk; that are very much greater than their widths, at least 100‑fold and from inorganic materials or minerals, such as asbestos greater. Fibers can be classified into one of three main group‑ found in older types of home insulation and glass in fiberglass ings depending on how they are produced: (1) natural fibers, and spun glass materials. Several examples of natural fibers (2) regenerated (sometimes called reconstituted) fibers, and (3) are shown in Figure 7.56. manmade or synthetic fibers. Examples of each of these types Plant‑based fibers may be either carbohydrate‑based are illustrated in Figure 7.55. or protein‑based. Many plant‑derived fibers are composed  7 Anatomical Evidence: The Outside Story 225 largely of the carbohydrate polymer cellulose, a complex sugar or polysaccharide molecule (“poly” meaning many and “sac‑ charide” meaning sugar). The chemical structure of cellulose, shown in Figure 7.57, consists of many smaller sugar units (the six‑membered rings) strung together to form a very long chain. These long chains can intertwine and chemically bond to one another through hydrogen bonds between adjacent strands to give a strong and sturdy fiber (Figure 7.58). Animal‑derived fibers are typically composed largely of protein, such as keratin or the silk‑related proteins. Like cellulose, these proteins are polymeric materials built from smaller units linked together, except in this case using amino acid building blocks. These fibers can be both very strong physically and highly resistant to chemical damage. Some can be remarkably elastic. Probably the most common ani‑ mal protein fiber is silk, obtained from the cocoons of silk moths. Silk proteins, mostly fibroin and sericins, are largely built from the amino acid glycine, making up to about 50%, which provides the highly desirable strength, sheen, and tex‑ ture of silk. Mineral fibers, such as asbestos, have a variety of com‑ FIGURE 7.56 Examples of natural fibers: (a) asbestos fibers, (b) positions and are primarily used for composites and building silk fibers from silkworm cocoons, and (c) jute rope fibers. components. They are so ubiquitous that they often appear in forensic investigations. Source: Images used courtesy Shutterstock.com. FIGURE 7.57 Structure of cellulose [(C6H10O5)n]. Hydrogen bonds FIGURE 7.58 Hydrogen bonds (dashed lines) holding together three strands of cellulose polymer (each cellulose strand is shown in a different color). 226 Introduction to Forensic Science 7.4.4 Regenerated Fibers modifications in the production process in 1924, a very stable, durable, and desirable form of rayon silk was first introduced Regenerated fibers are those made by chemically processing to the market. naturally occurring materials into fibers with new shapes and In the production of rayon and its analogs, cellulose from designed structures. Rayon and acetate are two very com‑ trees and other plants is first dissolved or suspended in a sol‑ mon examples of regenerated fibers made from cellulose vent and chemically purified and treated before being formed (Figure 7.59). into new threads and fibers through a variety of manufacturing Regenerated fibers can be classified as deriving from processes. In one common process for forming these fibers, either cellulose‑based or protein‑based starting materials, both the wood from trees is first chopped into small pieces that are typically processed from plants. The first commercial regener‑ chemically treated to remove all non‑cellulose components and ated fiber was rayon, originally called “artificial silk”. It was bleached to eliminate any coloration from the material. The discovered in 1855 and later produced on a large scale begin‑ cellulose is then dissolved in a basic solution, bathed in carbon ning in the 1890s. However, the early artificial silk was far disulfide (CS2), extruded from a showerhead‑like device (spin‑ different from the material we use today; through chemical neret), and ultimately stretched to produce the characteristic thin threads. The final stretching process helps to realign the long cellulose molecules along the length of the fiber. There are a number of new and increasingly important regenerated fibers that originate from plant or animal proteins rather than from cellulose. For example, the protein from corn (seins), soy (glycins), peanut (mainly arginine), or milk (casein) can be used to form strong, stable, and occasionally biodegrad‑ able fibers (Figure 7.60). A good example is soybeans, which form smooth, light, and soft fibers, similar to the natural fiber of cashmere. Some of these fibers have the advantage of being produced in an environmentally friendly fashion. 7.4.5 Synthetic Fibers Synthetic fibers are entirely prepared from small molecules, often petrochemicals (oil), rather than from natural fiber sources, and are formed through polymerization reactions that lead to long‑chain molecules. Common synthetic fibers include nylon, polyethylene, acrylic polyesters, PVC fiber, and poly‑ FIGURE 7.59 The preparation of changed forms of regen- urethane. The properties of synthetic fibers are controllable by erated cellulose fibers from dissolved cellulose in a solution of design and vary widely in structure. Schweizer’s reagent. Some synthetic polymers have special elastic properties Source: Used per Creative Commons Attribution‑Share and are called elastomers (e.g., spandex, polyurethane, neo‑ Alike 4.0 International. User: Perwincz. prene, and others). Silicones, compounds composed of chains FIGURE 7.60 (Left) Regenerated carbon fiber and (Right) regenerated cotton and synthetic polyurethane fibers woven together to form an elastomer. Source: Right, Susumu Nishinaga/Science Photo Library. Used with permission.  7 Anatomical Evidence: The Outside Story 227 of silicon, carbon, and oxygen atoms, make particularly good of this, a typical polymer made up of 10,000 monomers strung elastomers since the chemical backbone chain is very flexible. together would be comparable in length‑to‑thickness ratio to Lycra (spandex) is a polyurethane polymer that has both rigid a 6‑in.‑thick rope (15 cm) that was over a mile long (1.6 km). and flexible subunits repeated in its chain structure. The com‑ Importantly, polymers and plastics are everywhere we bination of these subunits provides a material with strength look today and, therefore, are very frequently part of crime from the rigid parts and elasticity from the flexible units that scenes, emergency medical apparatuses to aid victims, and can “unwind” (Figure 7.60, Right). numerous other aspects of forensic investigations. Synthetics are among the strongest of the known fibers. One convenient way to subdivide the vast array of known Additionally, many regenerated and synthetic fibers are ther‑ polymers already described is to consider natural polymers and moplastic – they melt or soften easily. This allows them to synthetic polymers. Chemically, natural polymers include bio‑ be easily molded into a variety of shapes by heating and then polymers, such as proteins, polysaccharides, nucleic acids, and cooling (e.g., pleats, creases, containers, solid objects, and inorganic polymers, such as asbestos and graphite. Synthetic many more). A plastic material, by definition, is simply some‑ polymers are most often prepared by linking together a variety thing that can be shaped or molded. Today, however, the term of small organic monomers. plastic has become synonymous with synthetic thermoplastics. Polymers display an amazing array of properties that are put to an equally enormous variety of uses, ranging from soft pliable materials to extremely hard, structural components. 7.4.6 Polymers Polymers now fulfill needs that no other materials can, from artificial skin to high‑strength composites. There are, how‑ In Chapter 4 on DNA, the general idea of polymeric molecules ever, a few key features that dictate the observed properties of was presented. Fibers, whether natural, regenerated, or syn‑ a polymer. Understanding these features helps us identify the thetic, are typically composed of long polymer molecules, of specific polymer that might have played a role in a crime. which DNA is just one very important specific example. Probably the most important feature is the identity of the Polymers are, by definition, long‑chain molecules that small monomer molecules that are linked together to form are built by stringing together many smaller subunits, called a polymer strand. The chemical structure of the individual monomers. These chains are typically very long. To get a sense monomers dictates what is possible in the full polymer. A few FIGURE 7.61 Various monomers that combine to make polymers (unlabeled junctures between the lines indicate carbon atoms). 228 Introduction to Forensic Science examples of monomers, along with the polymers that they The other most common way to form a polymer from form, are shown in Figure 7.61 and include: monomers occurs through a reaction called condensation, a reaction that involves the loss of a small molecule, such as water, Amino acids, which form proteins. from the reaction. For example, the reaction of terephthalic Sugar molecules (such as glucose), which form acid with ethylene glycol results in the elimination of H2O polysaccharides. to form the condensation polymer polyethylene terephthalate Nucleotides (composed of a phosphate, sugar, and (Figure 7.63). To say that this type of reaction is important in nitrogen base), which form DNA and RNA. forming needed biopolymers would be a huge understatement. Ethylene, which forms polyethylene. Condensation reactions are used to build proteins from amino An organic di‑acid molecule coupled with a acid building blocks, polysaccharides from simple sugars, and diamine, which forms nylon. DNA from individual nucleotides (Figure 7.64). Clearly, with‑ Carbon, which forms diamond, buckminsterfuller‑ out this single type of polymerization reaction, life would not ene, and nanotubes. be possible as we know it. Overall, the properties of polymer molecules are con‑ Today, most of our synthetic polymers are composed of just trolled by several chemical features including: five monomers: ethylene, vinyl chloride, styrene, propylene, and terephthalic acid (when reacted with ethylene glycol). The Chemical composition of the monomers. structures of these five small molecular monomers and some Formation of straight or branched chains. of the objects made from them are shown in Figure 7.62. The Length of the chains. first four of these monomers form long chains through the for‑ Orientation of the monomers within the chains. mation of direct monomer‑to‑monomer linkages, a chemical Bonding between the chains. process called polymerization that is brought about by cata‑ Introduction of co‑polymers. lysts (special chemical reagents that can cause a chemical reac‑ tion to occur or to accelerate without being ultimately changed Some monomers can only link to form a straight chain, like a itself). These reactions are often called addition reactions railroad train, while others can branch out, forming tree‑like since the net result is to simply add the monomers together structures. Their ability to branch strongly affects the chemical without the loss of any portion of the monomer. These reac‑ and physical properties of the resultant polymer. For example, tions account for millions of tons of polymers produced annu‑ high‑density polyethylene (HDPE) is made up almost entirely ally in the United States alone, with polyethylene being the of straight chains. This allows the chains to stack together very number one polymer produced. well to form dense, tightly packed materials, similar to the way FIGURE 7.62 (Above) The most common monomers for making synthetic polymers today are (Clockwise from Upper Left): ethylene, vinyl chloride, styrene, propylene, and terephthalic acid. (Below) Some of the plastic items made from these monomers. Source: Bottom, Shutterstock.com.  7 Anatomical Evidence: The Outside Story 229 Condensation Polymerization Reaction Loss of Water (condensation) Polymer-linking bond formation FIGURE 7.63 Formation of a polyester: the polymer polyethylene terephthalate is produced from a condensation reaction through the loss of water and the formation of an ester bond (R‑O‑C(=O)R′ where R and R′ are organic chemical groups). Amino Acid Amino Acid Tree stacking Wood stack similar to similar to stacking in LDPE stacking in HDPE Loss of H2O Protein Formation FIGURE 7.65 (Left) Schematic of the polymer stacking in high‑density polyethylene (HDPE) versus low‑density polyethyl- ene (LDPE) and (Right) a comparison with the analogous stacking FIGURE 7.64 Formation of a peptide bond, the bond linking of logs versus branched trees. amino acids together, to form a protein biopolymer. long boards in a lumberyard or straight logs can be efficiently stacked in a pile (Figure 7.65). Low‑density polyethylene (LDPE), on the other hand, is made up of branched chains that Styrene Polystyrene do not allow the individual chains to pack together very tightly. This would be similar to trying to stack trees with all of the branches still attached, resulting in an inefficient stack with lots of open airspaces between the tree trunks. The result of these kinds of packing is that HDPE forms very rigid, dense, and high‑strength materials, used in applications such as water pipes, snow boards, and storage sheds, while LDPE forms softer, low‑density, flexible, low‑melting polymers, found fre‑ quently in plastic bags, milk containers, and plastic laminate. With some monomers, the two “ends” of the building blocks where they connect together have different chemi‑ cal components. When they are assembled into a polymer, there are two ways that the building blocks can be assembled: head‑to‑head or head‑to‑tail, as illustrated in Figure 7.66. FIGURE 7.66 Orientation differences in forming synthetic poly- These two possibilities lead to different chemical and physical mers: head‑to‑tail versus head‑to‑head connections. 230 Introduction to Forensic Science properties of the polymer, although head‑to‑tail arrangements from just one type of monomer. The very popular plastic are far more common. wrap, used for preserving food because of its very low perme‑ The properties of polymers can often be changed by ability to gases and moisture that would speed up food spoil‑ building bridges between adjacent chains through a process age, is an example of a copolymer made from polyvinylidene called cross‑linking. This process is what usually happens chloride and other monomers such as acrylic esters. Many when a resin or polymeric precursor is cured or hardened variations on the copolymer idea have been developed for after it is applied in a soft or liquid form. During the harden‑ specific applications. ing process, the bridges are created between the polymeric strands to form a three‑dimensional lattice of interwoven strands and linkages throughout the material (Figure 7.67). 7.4.7 Forming Polymer Fibers These bridges can also occur at several size levels. Most com‑ monly, cross‑linking is considered at the molecular level, but Many methods have been developed over the years to form larger strands can also be cross‑linked at the macroscopic reconstituted or synthetic polymers into useful fibers. Probably level to give a three‑dimensional web‑like structure, as shown the most common, however, involves some type of extrusion for a cross‑linked styrene‑based polymer in Figure 7.68. The process (Figure 7.69). degree of cross‑linking imparts important features to the In this technique, the polymer(s) in a pliable form, such polymer. For example, permanent press fabrics have rela‑ as in a solution or as a viscous liquid, is forced through the tively few cross‑linkages, resulting in a soft and pliable fab‑ small openings of a showerhead‑like device called a spin‑ ric but one that can retain its shape. Rigid polymers, such as neret. The spinneret may have from just a few to hundreds of Bakelite (the world’s first synthetic plastic, used to produce holes of varying shapes. Often, the shapes of the small open‑ clocks, car parts, washing machines, and kitchenware), are ings dictate the cross‑sectional shape of the fiber produced heavily cross‑linked, forming exceptionally hard, inflexible, (polyurethane fibers in Figure 7.55). As the fiber is pushed out and brittle materials. through the holes, it solidifies to produce the filaments. Often, Polymers can also be made from a blend of different the fibers are stretched while they are hardening to align the monomers. The resulting polymer is referred to as a copoly‑ polymer molecules along the length of the fiber, producing a mer, in contrast to a homopolymer which is a polymer made stronger fiber. FIGURE 7.67 Cross‑linking of individual polymer molecules.  7 Anatomical Evidence: The Outside Story 231 FIGURE 7.68 Cross‑linked polymers: (Left) linear chains of thermoplastic polymer, and (Right) a three‑dimensional cross‑linked ther- mosetting polymer (cross‑linking points are shown as black circles). Such networks are usually insoluble and do not melt (the dimen- sion of a circle (monomer unit) is approximately 1 Å). Source: Used per Creative Commons Attribution‑Share Alike 3.0 Unported. 3.0. User: Cjp24. What is the composition of the fiber? This can often be answered through a chemical analysis of the fiber using the analytical tools described in later chapters. The goal is to determine the chemi‑ cal components that make up the fiber (the com‑ ponent monomers) and to determine the specific features of the molecular structure of the chains. This would involve discovering the identity of the monomer(s) employed, whether the sample is a copolymer or homopolymer, the relative orienta‑ tion of the monomers to each other, and the degree of cross‑linking formed between the chains. The chemical analysis would also determine the pres‑ ence of plasticizers and other additives included in the polymer to help it be more pliable or stable. A simple flow chart has been developed to aid in describing the chemical/structural composition of FIGURE 7.69 Fiber extrusion process (e.g., nylon, polyester, etc.) fiber, as shown in Figure 7.70. using two different polymers which, when extruded together, What are the physical properties of the fiber? This produces structured fibers with properties differing from the typically involves determining the melting prop‑ original fibers. erties (e.g., softening temperature, melting tem‑ Source: Used per Creative Commons Attribution 3.0 Unported, perature, glass transition temperature (Tg), and the User: CSIRO. sharpness of the melting point), the degree of crys‑ tallinity, the refractive index, and the chain length in the polymers in the fiber. Other information of 7.4.8 Forensic Analysis of Fibers interest might involve features such as birefrin‑ gence (whether the refractive index is the same in There are several important questions that are often asked as all directions of the fiber) and opacity (whether light part of forensic investigations when considering fibers, including can pass through the fiber). 232 Introduction to Forensic Science Fibers Natural Manmade Animal Vegtable Mineral Synthetic Natural polymer Other (asbectos) Polymer (earbon, glass metal, ceramie, etc.,) Seed Bast Leaf (cotton, (flax, (sisal, Alginate Rubber Regenerated Regenerated Cellulose coir, etc.,) hemp, abaca, (elastimer, Protein Cellulose Ester etc.,) etc.,) FTC, etc.,) (rayon) Silk Wool Hair Animal Vigetable Acetate Triacetate (sheep) (camel, cow, (casein) (arachin) horse, goat, etc.,) Viscose Cupro Modal Lyocell Polyolefm Polyvinyl Cmpds Polyurethane Polyamide Aramid Polyester Other Synthetic Polyethylene Polypropylene Segmented Non-segmented Polyurethane Polyurethane (spandex, etc.,) Acrylic Modacrylic Chlorofiber Vimyl Fluorofiber (PTFE, etc.,) (polyvinylchloride, polyvinylidene chloride) FIGURE 7.70 Flow chart for determining the classification of fibers. What is the shape of the fiber? This can usually be other items. Of particular importance is the use of fibers to best answered by observing the structure of the fiber form cloth. at the microscopic level. Both light and electron Cloth, or textile, is a network of fibers that can be shaped microscopic investigations are possible, including into a two‑dimensional layer for a variety of uses. While these comparison microscopic techniques to evaluate the two terms are often used interchangeably, they have subtly dif‑ similarities and differences between two fibers. ferent meanings; a textile is a material made from interlacing Is the fiber part of a larger piece of evidence? This fibers while the term cloth refers to a fabric that has been made refers to the possibility of the fiber being part of a into a finished piece such as a shirt or pants. Typically, textiles particular collection of fibers, such as a piece of are made from yarns, long segments of fibers that are twisted cloth, with the likelihood of dyeing and/or coloration or grouped together to form a relatively strong, interlocking of the fiber as part of a pattern or design on the cloth. array. Yarns are often formed by twisting shorter lengths of Are there any uniquely identifying features of the fibers together such that the manner of twisting can help iden‑ fiber? This involves looking for unique features of the tify a particular yarn. For example, the yarn can be character‑ fiber or cloth that would separate it from all other sim‑ ized by whether it is twisted clockwise or counterclockwise ilar samples, such as striations, cutting marks, torn (Figure 7.71), how tightly it is twisted (e.g., number of twists features, extrusion shapes, and other considerations. per inch), the number of fibers in the thickness of the yarn, and how it is colored. Importantly, yarns are often made by blend‑ ing together different types of fibers. For example, a textile 7.4.9 Collections of Fibers used in clothing might be a blend of 20% cotton, 30% wool, in Larger Pieces and 50% synthetic polymer. Yarns may be made stronger by taking smaller yarns and One of the key reasons why fibers are of such utility and so twisting them together to make even thicker units. For exam‑ commonly found in forensic investigations is their fabrication ple, taking two previously formed yarn strands and twisting into larger collections to form cloth, rope, paper, and many them together makes a thicker, stronger, 2‑ply yarn. The “ply”  7 Anatomical Evidence: The Outside Story 233 number indicates how many single spun yarns are twisted together to make the thicker yarn. Yarns are often woven together in intricate patterns to form cloth. An analysis of these weaving patterns can readily