Trace Evidence: Hair

1
Trace Evidence Hair

• Encountered at crime scenes
• Not good for individualization of physical
  evidence
• 1. No distinctive chemical properties
• 2. Although structural pattern exists, great
  amount of variation
• Hair provides corroborative evidence to place an
  individual at a crime scene
• DNA testing has linked a hair to an individual
• only if follicular tissue or root attached
• only if hair in particular growth phase
• analysis of mitochondrial DNA
• Combo of microscopic, genetic and ample control
  samples necessary-good? No, b/c cant
  distinguish b/w mDNA and hair structure

2
Morphology of Hair

• Cuticle
• Scale structure covering exterior of hair
• Seen with a scale mount
• Cortex
• Main part of the hair shaft
• Most forensic evidence pigment granules-size,
  arrangement, shape and color
• Medulla
• Looks like a central canal if present pattern
  continuous, interrupted, fragmented
• medullary index diameter of medulla relative
  to diameter of shaft expressed as a fraction
• Has shape which varies from species to species

3
Hair Growth

• Root produces the hair
• Phases of Growth
• 1. Anagen initial growth follicle actively
  producing hair had follicular tag
• 2. Catagen transition stage hair bulb shrinks
  in size
• 3. Telogen final growth hair falls out

4
Shaft of Hair extends from skin
Human Hair Microscopic Features
Caucasion Negroid Mongoloid

5
Human Medulla Patterns
interrupted
absent
continuous
6
Human Scale Pattern
Pattern of the cuticle
7
Human Feature For Comparison

• Body location
• Length of shaft
• Medullary index
• Diameter
• Presence of absence of medulla
• Distribution of shape and color intensity of
  pigment granules present in the cortex
• Artificial treatment dye
• Tip and Base of Hair

8
Human vs. Animal

• Medullary index less than 1/3
• Medulla has a shingle like appearance
• Large portion is cortex

• Medullary index greater than ½
• Medullar has a patterned shape
• Small portion is cortex