1. The study of important trace evidence
Hair, Fiber, and Paints
The study of important trace evidence

2. Morphology and Structure of Hair

3. Hair Morphology Con’t

4. Morphology: Cuticle
Protective coating made of overlapping scales, produce a characteristic pattern
Scales always point toward tip of hair
Not useful in individualizing human hair
Can be used for species identification

6. Morphology: Cortex
Made of spindle-shaped cells aligned in a regular array, parallel to the length of the hair
Embedded with pigment granules that give hair its color
The color, shape and distribution of the granules provide points for forensic comparison

7. Morphology: Medulla
canal like structure of cells that runs through the center of the cortex

8. Medullary Index
Measure of the diameter of the medulla relative to the diameter of the hair shaft
Usually expressed as a fraction
Humans: medullary index < 1/3
Animals: medullary index > 1/2

9. Medulla of Different Species

10. Forensic Analysis of Medulla
Presence of medulla varies quite a bit: even hair to hair
Human head hairs generally have no medulla or may be fragmented ones; except Mongoloid race whose medulla is usually continuous
Most animals have medulla that is continuous or interrupted
The shape of the medulla can help identify a species
Examples:
Most animals and humans: cylindrical
Cats: pearl shape
Deer: spherical occupying whole hair shaft

11. Identification and Comparison of Hair
Morphological hair characteristics do not yet allow individualization of a human hair to any single source
Hair when collected with an adequate number of standards/references can provide strong circumstantial evidence
Scale structure, medullary index, and medullary shape are most often used for hair comparison
Evidential value lies with degree of probability associated with a questioned hair and an particular individual
11 percent of all morphological hair matches are generally found to be non-matches—meaning microscopic hair comparisons are presumptive in nature—must be confirmed by DNA comparisons

12. Morphology: Root
Human hair grows in three developmental stages: anagen, catagen, and telogen phases

13. Root: Anagen Phase
Initial growth phase during which hair follicle is actively producing hair, phase may last 6 years, root is flame like in appearance
When pulled this root may contain a follicular tag (rich source of DNA)
Anagen hair root
Root w/ follicular tag

14. Root: Catagen Phase
A transition phase—hair grows at a decreasing rate for two to three weeks—elongated appearance as root bulb shrinks and is being pushed out of hair follicle
Catagen hair root

15. Root: Telogen phase
Hair growth has ended—root takes on a club-like appearance—during two-six month period, the hair will be pushed out of the follicle causing the hair to shed naturally
Telogen hair root

16. Important Forensic Questions
Can the body area from which a hair originated be determined?
Can the racial origin of hair be determined?
Can the age and sex of an individual be determined from a hair sample?
Is it possible to determine if a hair was forcibly removed from the body?
Are efforts being made to individualize human hair?

17. Fibers: Natural
Derived entirely from animal or plant sources Most prevalent plant fiber is cotton.
Its widespread use has made its evidential value almost meaningless
Cotton has a ribbon-like shape with twists at regular intervals
Animal sources include sheep (wool), goats (mohair, cashmere) and others

18. Man-Made Fibers
Fibers derived from either natural or synthetic polymers
The fibers are made by forcing polymeric material through the holes of a spinneret
Rayon and then nylon were the first two man-made fibers (year 1911)

19. Man-Made Fibers Con’t Regenerated Fibers Synthetic Fibers
Made from regenerated cellulose (wood or cotton pulp)
Include such fibers as rayon, acetate, and triacetate
Synthetic Fibers
Currently manufactured
Made from synthetic chemicals called polymers
Include such fibers as nylons, polyesters, and acrylics

20. Polymers Basic chemical substance of all synthetic fibers
Consist of long chains of repeating molecules. The repeating molecular units in the polymer are called monomers.
Often referred as macromolecules or “big” molecules
Countless varieties exist

21. ID and Comparison of Man-Made Fibers
Fabrics that can be fitted together at their torn edge are easy to match
Microscopic comparison of color and diameter
Comparison of lengthwise striations and pitting on the surface of a fiber
The shape of the fiber—ex. Wayne Williams case
Note: Combined factors of color, size, shape, microscopic appearance, chemical composition, and dye content make it very unlikely to find two different people wearing identical fabrics

22. Tools and Techniques to Aid in Comparing Fibers
Light infrared spectrophotometer—compares colors and chemical composition through spectral patterns
Chromatography—compares dye composition
Refraction—ID’s fiber by refractive index
Comparison microscope—reveals shape, coloring, pitting and striations

23. Forensic Examination of Paint
Paint evidence is frequently encountered in hit-and-run and burglary cases
Most examinations consist in comparing two or more paints to establish their origin
Often color, make and model of a vehicle can be determined

24. Paint Characteristics
Paint spread on a surface will dry into a hard film consisting of pigments and additives suspended in a binder
The binder provides the support medium for the pigments and additives.

25. Paint Characteristics
Modern automotive finishing consists of at least four coatings:
Electrocoat Primer: first layer, electroplated to the car—provides corrosion resistance—color from black to grey
Primer Surface: second layer, smoothes out and hides any seams on the car—color pigments are used to minimize contrast between primer and topcoats
Basecoat: third layer, provides the basic color and appearance of the car
Clearcoat: final coat, provides great appearance (glossiness) and protection for the car

26. Techniques to Aid in Paint Examination
Questioned (L) and known (R) specimens are compared side by side under a stereomicroscope for color, surface texture, and color layer sequence
*Note: Layer sequence is very important evidence: forensic scientists will try to match layers with respect to number and sequence of color
*Note: Layer structure alone will not provide enough information to be individualized to a single source
Chemical analysis of the paint’s pigments and binder composition provides further points of comparison.

27. Tools to Aid in Paint Examination
Gas chromatography is used to determine the chemical make-up of the binder material.
Infrared spectrophotometry is also used to determine the binder composition of paint.
Elements of the paint pigments can be identified with a number of techniques, including spectroscopy, neutron activation analysis, and x-ray diffraction
Using these techniques the odds against crime-scene paint originating from another randomly chosen vehicle is approximately 33,000 to one.