Trace Evidence: Hair Encountered at crime scenes Not good for “individualization” of physical...

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 can’t distinguish b/w mDNA and hair structure

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

Hair Growth

• Root –produces the hair

• Phases of Growth1. 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

Human Hair: Microscopic Features Caucasion Negroid Mongoloid

Shaft of Hair: extends from skin

Human Medulla Patterns

interrupted

absent continuous

Human Scale Pattern:Pattern of the cuticle

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

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