Chapter 11 - Hairs and Fibers PDF Summary

Saferstein, Richard, and Tiffany Roy. Criminalistics. (13th Edition). Pearson Education (US), 2020. CHAPTER 11 – HAIRS AND FIBERS Summary Hair is an appendage of the skin that grows out of an organ known as the hair follicle. The length of a hair extends from i...

Saferstein, Richard, and Tiffany Roy. Criminalistics. (13th Edition). Pearson Education (US), 2020. CHAPTER 11 – HAIRS AND FIBERS Summary Hair is an appendage of the skin that grows out of an organ known as the hair follicle. The length of a hair extends from its root or bulb embedded in the follicle, continues into a shaft, and terminates at a tip end. The shaft, which is composed of three layers—the cuticle, cortex, and medulla—is subjected to the most intense examination by the forensic scientist. The comparison microscope is an indispensable tool for comparing these morphological characteristics. When comparing strands of hair, the criminalist is particularly interested in the color, length, and diameter. A careful microscopic examination of hair reveals morphological features that can distinguish human hair from the hair of animals. Scale structure, medullary index, and medullary shape are particularly important in hair identification. Other important features for comparing hair are the presence or absence of a medulla and the distribution, shape, and color intensity of the pigment granules present in the cortex. However, microscopic hair examinations tend to be subjective and highly dependent on the skills and integrity of the analyst. Recent major breakthroughs in DNA profiling have extended this technology to the individualization of human hair. The probability of detecting DNA in hair roots is more likely for hair being examined in its anagen or early growth phase as opposed to its catagen or telogen phases. Often, when hair is forcibly removed, a follicular tag, a translucent piece of tissue surrounding the hair’s shaft near the root, may be present. This has proven to be a rich source of DNA associated with hair. Also, mitochondrial DNA can be extracted from the hair shaft. As a rule, all positive microscopic hair comparisons must be confirmed by DNA analysis. When questioned hairs are submitted to a forensic laboratory for examination, they must always be accompanied by an adequate number of standard/reference samples from the victim of the crime and from individuals suspected of having deposited hair at the crime scene. Forensic hair comparisons generally involve either head hair or pubic hair. Collecting 25 full-length hairs from all areas of the scalp normally ensures a representative sampling of head hair. Likewise, a minimum collection of 25 full- length pubic hairs should cover the range of characteristics present in this type of hair. In rape cases, care must first be taken to comb the pubic area with a clean comb to remove all loose foreign hair present before the victim is sampled for standard/reference hair. The comb should then be packaged in a separate envelope. The quality of fiber evidence depends on the ability of the criminalist to identify the origin of the fiber or at least to narrow the possibilities to a limited number of sources. Microscopic comparisons between questioned and standard/reference fibers are initially undertaken for color and diameter characteristics. Other morphological features that could be important in comparing fibers are striations on the surface of the fiber, the presence of delustering particles, and the cross-sectional shape of the fiber. The visible- light microspectrophotometer provides a convenient way to compare the colors of fibers through spectral patterns. Infrared spectrophotometry is a rapid and reliable tool for identifying the generic class of fibers, as is the polarizing microscope. Page 1 of 2  Saferstein, Richard, and Tiffany Roy. Criminalistics. (13th Edition). Pearson Education (US), 2020. CHAPTER 11 – HAIRS AND FIBERS Relevant articles of clothing expected to bear fiber evidence should be packaged carefully in paper bags. Each article must be placed in a separate bag to avoid cross-contamination of evidence. Scrupulous care must be taken to prevent articles of clothing from different people or from different locations from coming into contact. Such articles must not even be placed on the same surface before packaging. Fibers can be packaged in plastic containers or glassine folds placed inside manila coin envelopes. Page 2 of 2