HairsTrace Evidence

Hair as Physical Evidence■Class evidence■Removal indicates physical contact

between victim and perpetrator- Locard’s Principle

Hair as Physical Evidence■Not good evidence by itself.■Present with other evidence it becomes

stronger

Hair as Physical Evidence■Compare hairs by color and structure■Extract DNA from (if present) root for

comparison – Individual evidence. **Now hair is excellent evidence

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

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, or absent)■ Shape (human vs. animal)

Human Medulla Patterns

Interrupted Absent Continuous

Answers from Hair■Body area■Racial origin■Age and Sex (infant vs. adult, DNA from

root for gender)■Forcible removal (more sheath cells)

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

African American Asian

Caucasian (European)

Scissor-cut

Razor-cut

Broken

Burned

Dyed Hair

Lice Egg Case

DNA Evidence

■ Root: nuclear DNA

■ Shaft: mitochondrial DNA (mtDNA)

Growth Stages of the Hair:■ Anagen Stage:  The active growth phase of the

hair follicle. ■ Catagen Stage:  The transition period between

growth and rest.  Hair continues to grow, but at a decreasing rate.  The root bulb looks elongated from being pushed out of the follicle.

■ Telogen:  The rest period for the follicle.  The current hair is shed and no new growth takes place for a period of time.

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■Collect 50 hairs from suspect for

comparison. Not all hairs are the same

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