Chapter 8

Hairs & Fibers

Hair Appendage of the skin

Grows from hair follicle

Color & structure are important forensic features

Composed of 3 layers

Hair Shaft Layers

Cuticle Outside covering

Made of scales

Different species different scale patterns

Cortex

Main body of hair

Contains pigments that give hair its color

Medulla

Central canal

Varies in thickness (by species)

Not present in all hairs

Types of Medullas

Continuous:

Interrupted:

Fragmented:

Absent

Hair Growth

Occurs at root

Grows at a rate of 1 cm/month

3 phases: Anagen Catagen Telogen

Anagen Phase Initial growth (lasts 2 – 8 years) Follicle is actively making hair Root bulb flame shaped

**Follicular Tag Clear tissue around hair (near root)

BEST source of DNA

Catagen Phase

Growth slows

Follicle breaks down

Root bulb shrinks

Lasts 2 – 4 weeks

Telogen Phase Resting phase

Growth stops

Hair falls out

Root bulb club shaped

Identification of Hair

Determine whether it’s human or animal

Scale Structure Medulla Shape Medullary Index

**Problem Hairs can vary from one to the next in the same individual**

Comparison of Hair

View hairs with comparison microscope

Need standard/reference samples to compare the evidence to 50 head

24 pubic

Color, length, & diameter must match

Hair Evidence CAN Determine …

Place of body origin head, beard, pubic

Race but only sometimes

Hair Evidence CANNOT Determine …

Age or sex of an individual

Special Note

Hair is an important piece of

evidence, BUT is only 100%

when DNA is analyzed!!!

Fibers Can be natural or man-made

Important in homicides, assaults, & sexual offenses (Cross-transfer)

BUT mass production of fabrics has evidential value

Natural Fibers Come from animal or plant sources

Wool Sheep Cashmere Goat Mink

Cotton Plant Twisted, ribbon-like shape

                      

                      

Man-made Fibers

Rayon (1911) Nylon (1939) Polyester Acrylics Spandex

http://micro.magnet.fsu.edu/primer/techniques/polarized/gallery/pages/nylonlarge.html

Identification of Fibers Try to trace their origin

Examine color & diameter with comparison microscope

Look for striations & cross-sectional shape

Determine dye composition

                                      

Collection & Preservation

Remove fibers with clean forceps

Package articles of clothing separately

Use adhesive tape lifts on carpet, rugs, & bedding