Hair as Physical Evidence

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Presentation transcript:

Hairs Trace 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 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, 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 Broken Burned Razor-cut

Dyed Hair Lice Egg Case

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

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