Hair Evidence Forensic Science 1

What exactly is hair? An extension of the skin that grows out of an organ known as the hair follicle

Why is hair a good subject of a person’s identity? It contains DNA It resists chemical decomposition over time

Main Parts of Hair Cuticle: outer layer of hair that has scales that point towards the tip or end Cortex: inside the cuticle. This part of hair is responsible for hair color and hair shape Follicle: contains the richest source of DNA Root: responsible for hair growth Medulla: group of cells in the center of the hair. (Not always present)

Different Types of Medullas Continuous Interrupted Fragmented Absent

Medullary Index Diameter of the medulla divided by the diameter of the hair Usually is an indicator of species

Cross section view of hair

Can age, race, and sex be determined? Yes if we are able to extract the DNA from the hair If DNA is not present, it is possible to distinguish race based o differences in hair texture, shape, and color pigments

Trace Evidence: Hair Hair is the most common type of trace evidence It can identify a victim or suspect by extracting the DNA from it. Also it can be matched visually to known samples Cross transfer of hair: If there are hairs on someone else it raises the probability that those two people were in contact at some point

Hair Can Never Be the “Smoking Gun” Hair evidence cannot be the only piece of evidence that proves you guilty. It only places you at the crime scene at some point in time . More evidence is needed.

Collecting Hair at the Crime Scene Varies according to the circumstances of the investigation. 6 methods: Tweezers, Infrared Light, Tape, Vacuuming, Brushing garments, Bag method Combing and Clipping- all suspects in a crime are required to provide a minimum of 100 scalp hairs

View of Hair

Sites of Origin of Hair Scalp Eyebrow Facial Hair Underarm Body Pubic

Examining Hair Under the Microscope Looking at the shape and type of medulla Patterns in the color pigments Shape of the scale structures Hair grows at a constant rate of roughly 1mm a day !

Cross Section of Hair

Why identify the medullary index? Main purpose: distinguishes animal from human hair Animal Medullary Ratio: more than ½ (larger) Human Medullary Ration: less than 1/3 (fairly small if even present) Most human hair is either absent (no medulla) or interrupted Most animal hair is fragmented or continuous

Looking at the cortex and scale structures Cortex: looking for pigment granules and air bubbles when comparing one hair from another Cuticle Scale Structures: Used to determine species. There are 3 types- coronal (animal only), proximal (animal only), imbricate (human only)

3 Stages of Hair Growth Anagen: hair is actively growing (can last for up to 6 years) Catagen: root becomes elongated (can last for several weeks) Telogen: root becomes clubbed shaped (can last up to 6 months)

When hair is of little use in a crime Domestic disputes or murders where the victim and suspect lived together.