Trace Evidence

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Trace Evidence
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What do you think trace evidence is?

• Materials that are small enough to be easily
  overlooked by a crime scene investigator
• They are so small they can be transferred
  (exchanged) by contact or in the air by air
  currents!

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Locards exchange Principle?

• When 2 objects come in contact with each other, a
  cross-transfer of materials occurs

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Types of Trace evidence

• Hair
• Fibers threads
• Metals
• Paint other building materials
• Soil, rocks, minerals, debris
• String, rope, containers
• Wood plant material

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Anatomy of Hair

• Root (internal end)
• Medulla
• Inner core
• May or may not be present
• Cortex main shaft surrounding the medulla
• Cuticle scaly outer covering
• Tip (external end)

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Medulla Patterns

1. Continuous a solid line
2. Interrupted broken at regular intervals, like
   the dotted yellow lines on a road
3. Fragmented broken, but not in a regular pattern
4. Absent

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Anatomy of Hair
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Human, cat, Dog, and Mouse Hair
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What can hair tell us?

• We know it can tell us whether the hair is human
  or not.
• If human
• Race
• Pulled out or fell out?
• Part of the body it came from
• How it was cut or dressed
• If animal, what species?

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Phases of Hair Growth
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Location of Origin

• Scalp hair
• Little diameter variation
• More uniform distribution of pigment
• No medulla or fragmented
• Pubic hair
• Short and curly
• Wide variations in diameter
• Continuous medulla
• Beard hair

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Collecting the Evidence

• About 40-50 samples from the scalp
• About 24 full-length pubic hairs
• Need entire hair
• Variations in color and other features alng
  length of hair
• Collected how???

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Hair Analysis at Work

• Ennis Cosby
• Central Park Jogger
• Microscopic analysis vs. DNA analysis

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Hair Needed!

• Bring in samples of pet hair!
• Try to find hairs that have fallen out. (Where
  should you look?)
• Beard hair anyone?