1. Hair Evidence
Forensic Science 1

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

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

4. 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)

5. Different Types of Medullas
Continuous
Interrupted
Fragmented
Absent

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

7. Cross section view of hair

8. 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

9. 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

10. 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.

11. 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

12. View of Hair

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

14. 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 !

15. Cross Section of Hair

16. 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

17. 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)

18. 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)

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