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Hair as Physical Evidence

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Presentation on theme: "Hair as Physical Evidence"— Presentation transcript:

0 Hairs Trace Evidence

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

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

3 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

4 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

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

6 Hair Diagram

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

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

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

10 Cortex: Hair Pigmentation

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

12 Human Medulla Patterns
Interrupted Absent Continuous

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

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

15 Racial Origin African American Asian Caucasian (European)

16 Scissor-cut Broken Burned Razor-cut

17 Dyed Hair Lice Egg Case

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

19 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.


21 Hair as Forensic Evidence

22 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

23 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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