Fingerprints Notes PDF

Fingerprints Skin ○ Skin is the largest organ system in the human body (25 pounds) Skin is a part of the integumentary system which contains hair, skin, and nails ○ 3 layers Epidermis - outer layer...

Fingerprints Skin ○ Skin is the largest organ system in the human body (25 pounds) Skin is a part of the integumentary system which contains hair, skin, and nails ○ 3 layers Epidermis - outer layer Stratum corneum which is 25 to 30 layers of cells Thicker in palms and feet Contains melanin, fingerprints, palm prints, footprints, and lip prints Dermis - middle layer The protein layer in which hair follicles, sebaceous (oil), sweat, and scent glands Blood vessels and receptor cells are present Hypodermis (subcutaneous layer) Fat and connective tissue containing larger blood vessels and nerves Fingerprints ○ Fingerprints consist of ridges and furrows Ridgetop of the fingerprint pattern Furrow - lower valet of the fingerprint pattern ○ The patterns that are formed by ridges and furrows do not normally change throughout a person's life. ○ Exceptions Skin disease - psoriasis, eczema, skin cancer, etc Drugs - anti-cancer drug Capecitabine; causes fingerprints to disappear Scars - cause fingerprints to become very easy to identify once on record ○ Fingerprint patterns Fauids - first proposed identification system Henry - features of this classification system still used today in IAFIS Arch - 5% of population Loop - 65% of population Whirl - 10% of population ○ Fingerprint Comparison Level one Loops, whorls, and arches are identified as the main features ○ Loop patterns have 1 delta and 1 core ○ Whorl patterns have 2 deltas ○ Arch patterns have no deltas  Loops can be plain radical or Ulta Whorms can be plain, double-loop, accidental, or central pocket loop Level two Minutiae - intricate specified differences Level three Pore matching - more detailed investigation ○ Visible prints can be seen with the eyes Plastic or impression prints - fingerprints may be left in a soft pliable substance. Ex. clay, window putty, wet paint, wax, soap, tar, etc Patent prints - usually made in a visible substance Ex. ink, grease, blood, etc ○ Nonvisible prints - are not visible without aid. Oil, water, and amino acids can be transferred to an object or surface but are not visible. Fingerprint residue is mostly water. ○ Techniques for making latent prints visible Dusting for prints A fine powder is applied using a brush ○ Powders can be colored, magnetic, or fluorescent Ninhydrin A chemical that reacts with amino acids to form a purplish blue fingerprint image (slow process unless heated) Iodine Reacts with oils forming a brown image Cyanoacrylate (superglue) Used in a fuming chamber Reacts with amino acids to form a white image ○ Preserving fingerprints - once the prints are found or made visible it is important to record this evidence. Lifting prints: Cellophane tape can be used to remove a print from a surface and apply it to a card for permanent storage. Pinnascopy - ear shape patterns can be found on windows, doors, and mirrors. Cheiloscopy - lip groove patterns ---- Hair and Cloth Fibers Trace Evidence Hair analysis ○ Hair - grows from a follicle in the skin of only mammals Great diversity within species Fur is the hair of non-human mammals DNA is only present when part of the hair follicle is present (skin tag attached) 80-90% protein (mostly keratin and melanin) Keratin provides structure (long chains of amino acids) Melanin provides color Hair structure diagram ○ Cuticle - outermost layer - resembles shingles or scales Most susceptible to environmental factors and damage Patterns Coronal - crown-shaped (bats) - not soft Spinois - petal-shaped (minks) - very soft Imbricate - shingle-shaped (humans) ○ Cortex - the middle layer - gives hair elasticity It contains melanin and moisture ○ Medulla - innermost layer - center of the hair shaft It contains spongy cells that form a pattern specific to a species In humans, cells can be absent forming an empty canal Ethnic differences in hair structure ○ Asian (mongoloid) - round cross-section, greater diameter, straighter and thicker ○ Caucasian (caucasoid) - oval cross-section, able to bend and stretch, straightish but able to curl ○ African (negroid) - flat oval cross-section, ribbon-like, easily forms a tight curl Fiber Analysis ○ Fibers - long thin filaments whose length exceeds their width by 100+ times - structure and function similar to hair 3 main types Natural fibers ○ Ex. wool Regenerated fibers ○ Ex. thread Synthetic fibers ○ Ex. plastic Tend not to give hair as an answer to fibers since it isn't always true ○ Natural fibers - the first fibers used by man  Plant sources: Cotton for cloth Wood for paper Hemp for rope Living sources: Insects for silk Catgut for string Spiders for silk Animal fur for wool Natural fibers burn ○ Regenerated fibers - most made from cellulose and manipulated chemically by man Rayon and acetate are regenerated fibers ○ Synthetic fibers - made from petrochemicals Formed through polymerization (PVC) Common fibers are nylon, polyurethane, acrylic polyesters Elastomers are polymers with elastic properties Ex. spandex, polyurethane, and neoprene Synthetic fibers are woven Synthetic fibers melt Forensic questions to ask about Fibers ○ Which group of fibers does our evidence belong to? ○ How were the polymer chains produced? Spun or chemical polymer ○ What type of pattern exists in the fibers? Tells if natural or synthetic ○ What type of weaving pattern exists? ○ Does a dye lot match? ○ Does a tear or cut match the rip found at the scene?