1. Trace Evidence 1: Hairs & Fibers
Chapter 10
Forensics 2011

2. Forensic Examination of Hair
Hair is usually considered class evidence
If the hair follicle is included then DNA can be found and it becomes individual evidence
Hair is good for forensics because it resists chemical decomposition and retains its structure over a long period of time.

3. Morphology of Hair Hair grows out of a hair follicle
The shaft is what is usually studied in crime labs and has 3 parts:
Cuticle
Cortex
Medulla
Page 357 Figure 10-1

4. The Cuticle The stability of hair is because of its cuticle
The scale structure covering the exterior of the hair
Formed by overlapping scales that point towards the tip end of each hair
The scale pattern formed helps identify the species that the hair came from
Page 358 Figure 10-2
Can make a ‘cast’ of the hair shaft to see an impression of the cuticle
Done by placing hair in clear fingernail polish

5. The Cortex The cortex is protected by the cuticle
The cortex contains the pigments that give hair its color
The cortex is studied by mounting it in liquid with a similar refractive index to maximize the amount of light that goes through it

6. The Medulla
Collection of cells that run up the center of the hair shaft
Medullary index – compares diameter of medulla to diameter of hair
Helps determine species.
The medulla can vary from person to person and even from hair to hair
The medulla can be continuous, interrupted or fragmented – p 359 Figure 10-3
The shape of the medulla can also vary – p 360
Humans – cylindrical animals – pattern shape
Humans have a MI of 1/3. for most animals it is ½ or more
Shape of medulla – cats = string of pearls, deer = spherical cells the entire length

7. The Root
The root works with the follicle and produces hair and continues its growth
3 stages of hair growth
anagen phase – initial hair growth. Root is attached to hair follicle. If pulled out a follicular tag may be attached with DNA
Catagen phase – root not attached to follicle anymore as hair continues to grow
Telogen phase – hair starts to fall out

8. Identification & Comparison of Hair
Reasons to examine hair evidence from a crime:
Animal or human?
Does it compare to our reference samples?
Its very important for the examiner to have access to collections of reference samples and databases AND for them to have experience in hair examination

9. Factors in Comparison of Hair
Easy to determine the species the hair came from. Comparing WITHIN that species is harder
A criminalist tries to match hair based on:
Color (natural or dyed)
Length
Diameter
Medulla appearance

10. Microscopic Examination of Hair
Several hairs compared under a microscope to a reference sample
For a long time this was the only way to look at hair, as class evidence
An FBI study showed that 11 % of hairs “matched” microscopically DID NOT match according to DNA
Page 363 – Case Study

11. Important Questions about Hair Examination - 1
Can the body area from which a hair originated be determined?
Yes! Pigments and texture of hair differs from place to place on the body.
Can the racial origin of hair be determined?
Almost always, particularly negroid vs causcasian hair
Can the age or sex be determined from hair?
Only works for infant hair (for age)

12. Important Questions about Hair Examination - 2
Can you tell if hair was forcibly removed?
Sometimes. If a hair is yanked out it will sometimes contain part of the follicle.
Can we individualize human hair?
We are trying to
If hair root or follicle is intact nuclear DNA can be assessed
If not, sometimes mitochondrial DNA can still be found, but isn’t 100% individualized

13. Collection & Preservation of Hair Evidence
Important to collect the entire length of the hair
Properties may change along the length
Collection of reference samples from every body area and every suspect/victim is VERY important

14. Forensics Examination of Fibers
Fibers – come from fabrics and clothes
The value of fibers rests on the abilities of the criminalist to narrow down their origin
Two Types of Fibers
Natural – from a plant or animal source
Manufactured (man-made) – made from polymers

15. Natural Fibers Examples: Identified and Compared much like hairs
Wool, mohair, cashmere, etc
Also includes fibers from furs
Identified and Compared much like hairs
Most common is cotton
Cotton has distinguishing characteristics
P 368 Figure 10-8

16. Manufactured Fibers First introduced in 1911 with rayon
They have lots of trade names so ‘generic’ names are also used for general ID
Page
The first man-made fibers were made by breaking cotton or wood pulp into pure cellulose and treated chemically.
Synthetic fibers (like nylon) are made from polymers

17. Polymers
Many things are made from polymers (plastic, rubber, paints, adhesives, etc)
Polymers are made from linking molecules (monomers) in a long strand
Different properties can be made by using different polymers
Many natural fibers (cotton and hair) are made from natural polymers. (starch)
P 372 Figure 10-10
Nylon was made when a stirring rod was used to mix a thick material. When the rod was lifted a long strand connected the rod to the material. This strand was found to be very strong and very long.

18. Microscopic Examination of Fibers
Compare color and diameter
Important to compare the dyes as well
May also compare cross-sections to compare shapes of the fibers
P 373 Figure 10-12
Fiber shapes are different depending on how they were extruded (pulled)

19. Analyzing Chemical Composition
First must know WHAT the fiber is
Sometimes there are subclasses within a generic group, like nylon 6, nylon 11 etc.
There are many tests available, but a criminalist may only have a single fiber for all of their tests

20. Birefringence
A polymer is ‘spun’ out of a liquid and usually has all of the monomers lined up, like the atoms in a crystalline solid
P375 Figure 10-14
This causes the fibers to show specific colors when looked at under polarized light
P 376 Figure 10-15

21. Infrared Absorption
Polymers inside of fibers absorb infrared light in specific, known patterns
Very fast and easy way to identify at least the generic class of the fiber

22. Significance of Fiber Evidence
There is no analyzing that will say two fibers 100% for sure came from the same source
However, like all class evidence, enough of it together leads to a high probability
Still important to have other types of physical evidence to link the suspect and the crime

23. Collection & Preservation of Fiber Evidence
Fiber evidence is easily overlooked because it is so small
An investigator usually has to collect potential “carriers” of fiber evidence
Clothing, carpets, rugs, bedding
P 380 – Case Study