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)

• 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

• 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?

• 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 Wilkes-

Barre

Human Hair

• 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

• 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