Hair & Fibers
Class vs. Individual Evidence
• Hair is considered class evidence unless
DNA can be isolated from the root.
Remember:
Class evidence can only be connected to a
group
Individualized evidence can be connected to a
unique source.
Locard’s principle
• When two objects come into contact,
material is exchanged.
• How much material is transferred is
affected by
• Intensity of contact
• Duration of contact
• Type of surfaces
Questions to ask about trace
evidence (hair and fibers)
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1. What is it?
2. Man-made or natural?
3. What is its source?
4. How common is it?
5. Can it be identified to a single source?
Equipment
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Stereomicroscope
Compound microscope
Phase contrast microscope
Scanning electron microscope
Comparison Microscope
FTIR- Fourier Transform Infra Red
Spectrophotometer
• GC- Gas chromatograph
Why is human hair useful in
forensics?
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Sheds easily
Clings to clothes
Lasts for long periods of time
Toxins (esp. heavy metals) are deposited
in hair. You can estimate the time of
poisoning based on the growth rate of
hair)
– Case study: Robert Curley case from WilkesBarre
Human Hair
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scalp
pubic
eyebrow & eyelashes
beard
chest
arm
leg
Structure of Hair
• Follicle= pocket of cells where hair grows
• Cuticle
• Cortex
• Medulla
1. Cuticle- overlapping scales always point
up the shaft of the hair
2. Cortex- internal body, pigments
3. Medulla- inner core
– Smaller in humans than in animals
Types of cuticles
a) Coronal – common in mice, rats
b) Spinous(petal) – triangular shape, found
in cats - makes cat hair stick to other
materials easily
c) Imbricate (flat) – humans
Cortex
• Contains pigment of the hair
Medulla Types
• Solid or continuous
• Interrupted
• Fragmented
How to match hairs
• Consider:
1. color and width
2. medulla type
3. cuticle type
4. shape of hair in cross section
Hair in cross section
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Armpit ----- oval
Beard ----- triangular
Head ----- round
Eyelashes and brows ----- taper
Sources of Animal Hair
• Living animal
• Pelt
• Wool sweater
• Often pet hair transferred during crime
Fibers
• Small, elongated pieces of material used
to make:
– Cloth
– Carpet
– Paper
– Cardboard
– Rope
– String
Fibers
• Classification:
a) Natural- animal hairs (wool)
- excrement (silk)
- plant (cotton)
- mineral (asbestos)
b) Man-made
nylon
polyester
rayon
Fibers
• Sorted by:
– Color
– Fluorescence
– Thickness
– Water retention
– Cross-section
– FTIR
– Chromatography of dyes