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Hairs Trace Evidence. Hair as Physical Evidence ■ Class evidence ■ Removal indicates physical contact between victim and perpetrator- Locard’s Principle.

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Presentation on theme: "Hairs Trace Evidence. Hair as Physical Evidence ■ Class evidence ■ Removal indicates physical contact between victim and perpetrator- Locard’s Principle."— Presentation transcript:

1 Hairs Trace Evidence

2 Hair as Physical Evidence ■ Class evidence ■ Removal indicates physical contact between victim and perpetrator- Locard’s Principle

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

4 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

5 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

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

7 Hair Diagram

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

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

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

11 Cortex: Hair Pigmentation

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

13 Human Medulla Patterns InterruptedAbsent Continuous

14 Answers from Hair ■ Body area ■ Racial origin ■ Age and Sex (infant vs. adult, DNA from root for gender) ■ Forcible removal (more sheath cells)

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

16 Racial Origin African AmericanAsian Caucasian (European)

17 Scissor-cut Razor-cut Broken Burned

18 Dyed Hair Lice Egg Case

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

20 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.

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22 Hair as Forensic Evidence

23 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

24 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


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