Hairs Trace Evidence.

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Presentation transcript:

Hairs Trace Evidence

Hair as Physical Evidence Class evidence Removal indicates physical contact between victim and perpetrator Strong evidence to place individual at crime scene Compare hairs by color and structure Extract DNA from root for comparison

Characteristics of Hair Appendage of the skin Grows out of the hair follicle Length of hair extends from follicle  shaft  tip Follicle (root) contains DNA

Function of Hair Regulate body temperature (insulation) Decrease friction Protect against sunlight Sense organ

Hair Shaft Three layers: Cuticle: surface of hair Cortex: main body, contains pigment Medulla: hollow core

Hair Diagram

Cuticle : Outer Layer Transparent, outer layer Scales point down from younger end towards older ends of hair

Cuticle : Scale Patterns Human Hair Bat Hair Mink Hair Human or Animal Hair

Cortex: Color Layer Largest part of hair shaft Melanin = pigment granules

Cortex: Hair Pigmentation

Properties of the Medulla Medullary index (ratio of medulla:shaft) Pattern (continuous, interrupted, fragmented, or absent) Shape (human vs. animal)

Human Medulla Patterns

Answers from Hair Body area Racial origin Age and Sex (infant vs. adult, DNA from root for gender) Forcible removal (more sheath cells) Individualize hair (nuclear DNA in root or mitochondrial DNA from shaft)

Body Area Head (scalp) Eyebrows and eyelashes Beard and mustache Underarm Auxiliary or body hair Pubic hair Pubic Hair Beard Hair Limb Hair

Mongoloid (Asian) Hair Racial Origin Negroid (African) Mongoloid (Asian) Hair Caucasian (European)

Scissor-cut Broken Burned Razor-cut

Dyed Hair Lice Egg Case

DNA Evidence Shaft: mitochondrial DNA (mtDNA) Root: nuclear DNA

Hair as Forensic Evidence

Hair Collection Collected from crime scene by plucking, shaking and scraping surfaces Use tape over small surfaces Vacuum large surfaces Initial analysis performed under compound microscope

Testing For Chemicals Neutron activation analysis (NAA) – identify 14 different elements in hair Antimony, argon, bromine, copper, gold, manganese, silver, sodium, zinc Hair grows about 1.3 cm per month – calculate timeline for exposure to toxins or poison