HairsTrace 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

Mink Hair

Bat 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

Racial Origin

Negroid (African) Mongoloid (Asian) Hair

Caucasian (European)

Scissor-cut

Razor-cut

Broken

Burned

Dyed Hair

Lice Egg Case

DNA Evidence

Root: nuclear DNA

Shaft: mitochondrial DNA (mtDNA)

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