1. Trace Evidence
HAIR, FIBERS & PAINT

2. Introduction
Hair is encountered as physical evidence in a wide variety of crimes.
Although it is not yet possible to individualize a human hair to any single head or body through its morphology, it still has value as physical evidence.
When properly collected and submitted to the laboratory accompanied by an adequate number of standard/reference samples, hair can provide strong corroborative evidence for placing an individual at a crime scene.

3. Morphology of Hair
Hair is an appendage of the skin that grows out of an organ known as the hair follicle.
The length of a hair extends from its root or bulb embedded in the follicle, continues into a shaft, and terminates at a tip end.
It is the shaft, which is composed of three layers—the cuticle, cortex, and medulla—that is subjected to the most intense examination by the forensic scientist.

4. Morphology of Hair

5. Cuticle and Cortex
The cuticle is the scale structure covering the exterior of the hair.
The scales always point towards the tip of the hair.
The scale pattern is useful in species identification.
The cortex is the main body of the hair shaft.
Its major forensic importance is the fact that it is embedded with the pigment granules that impart hair with color.
The color, shape, and distribution of these granules provide the criminalist with important points of comparison among the hairs of different individuals.

6. Cuticle Covers the exterior of the hair.
The scales always point towards the tip of the hair.
The scale pattern is useful in species identification.

7. Cuticle Formed by overlapping scales points toward tip of hair
specialized keratinized cells (hardened)
Paint on pencil

8. Cuticle
Scale patterns can be used for species ID

9. The main body of the hair shaft.
Cortex
Embedded with pigment granules, imparts hair color
The color, shape, and distribution of these granules provide the criminalist with important points of comparison among the hairs of different individuals.
Central core
Wood of pencil
The main body of the hair shaft.

10. Medulla
The medulla is a cellular column running through the center of the hair.
The medullary index measures the diameter of the medulla relative to the diameter of the hair shaft.
Humans: Medulla generally occupies diam. less than ⅓ the shaft
Animals: Medulla generally occupies diam. of ½ or greater.
The medulla style may be: continuous, interrupted, fragmented or absent.
The presence of the medulla vary from individual to individual and even among hairs of a given individual.
Medullae also have different shapes, depending the species.

11. Medulla A collection of cells appearing like a central canal
Medullary Index
comparison of medulla diameter to shaft diameter
Graphite in pencil

12. The medulla may be continuous, interrupted, fragmented, or absent.
Medulla Patterns
The medulla may be continuous, interrupted, fragmented, or absent.
The presence of the medulla varies from individual to individual and even among hairs of a given individual.
Medullae also have different shapes, depending the species.

13. Root
The root and other surrounding cells in the hair follicle provide the tools necessary to produce hair and continue its growth.
When pulled from the head, some translucent tissue surrounding the hair’s shaft near the root may be found. This is called a follicular tag.
By using DNA analysis on the follicular tag, the hair may be individualized. (Ennis Cosby murder-killer ID thru DNA of hair)

14. Questions the Forensic Scientist asks
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?
Can DNA individualize a human hair?

15. Hair and DNA
Recent major breakthroughs in DNA profiling have extended this technology to the individualization of human hair.
The probability of detecting DNA in hair roots is more likely for hair being examined in its anagen or early growth phase as opposed to its catagen (middle) or telogen (final) phases.
Often, when hair is forcibly removed a follicular tag, a translucent piece of tissue surrounding the hair’s shaft near the root may be present.
This has proven to be a rich source of nuclear DNA associated with hair.

16. Hair and Mitochondrial DNA
Mitochondrial DNA can be extracted from the hair shaft.
Mitochondrial DNA is found in cellular material located outside of the nucleus and it is transmitted only from the mother to child.
As a rule, all positive microscopical hair comparisons must be confirmed by DNA analysis.

17. Collection and Preservation
As a general rule, forensic hair comparisons involve either head hair or pubic hair.
The collection of 50 full-length hairs from all areas of the scalp will normally ensure a representative sampling of head hair.
A minimum collection of two dozen full-length pubic hairs should cover the range of characteristics present in pubic hair.
Hair samples are also collected from the victim of suspicious deaths during an autopsy.

18. HAIR
Hairs indicating forced (left) and natural (right) removal.

19. Matching Hairs ID w/ Comparison Microscope

20. Naturally Shed Hairs, i.e., Combing: Undamaged Roots, club-shaped

21. Forcibly Removed Hair from the scalp Stretches and Damages the Root

22. Forcibly Removed Hairs MAY have tissue attached.

23. ANIMAL: Muskrat Hair

24. ANIMAL: Deer Hair

25. HUMAN: Head Hair (razor-cut)

26. HUMAN: Head Hair (split)

27. HUMAN: Head Hair (cut tip)

28. HUMAN: Pubic Hair

29. HUMAN: Caucasian or European Hair

30. HUMAN: Mongoloid or Asian Hair

31. HUMAN: Negroid or African Hair

32. Is It Human or Animal? Morphological characteristics Scale patterns
Medullary Index
human hair generally <1/3
animal hair >=1/2
Medullary Shape
human normally cylindrical

33. Comparing Strands
Comparison Microscope: tool for comparing the morphological characteristics of hair.
When comparing strands of human hair, the criminalist is particularly interested in matching the color, length, and diameter.
Microscopic exam of hair reveals morphological features that can distinguish human hair from the hair of animals.
Scale structure, medullary index, and medullary shape are particularly important in animal hair ID.

34. Comparing Strands Important features for comparing human hair are:
the presence or absence of a medulla.
the distribution, shape, and color intensity of the pigment granules present in the cortex.
The most common request is to determine whether or not hair recovered at the crime scene compares to hair removed from the suspect.
However, microscopic hair examinations tend to be subjective and dependant on the skills and integrity of the analyst.

35. Hair Comparison Uses comparison microscope color length diameter
presence or absence of medulla
distribution, shape & color intensity of pigment granules
dyed hair has color in cuticle & cortex
bleaching removes pigment & gives yellow tint

36. Collection of Hair Evidence
Questioned hairs must be accompanied with an adequate number of control sample hairs
from victim
from others suspected of depositing hair at crime scene
Representative control samples
50 full-length hairs from all areas of scalp
24 full-length pubic hairs

37. Collection of Hair Evidence
The most common request is to determine whether or not hair recovered at the crime scene compares to hair removed from the suspect.
However, microscopic hair examinations tend to be subjective and highly dependant on the skills and integrity of the analyst.

38. Hair is Class Evidence Can often determine body area of origin
Can often determine racial origin
Negroid
kinky with dense uneven pigment
flat to oval in shape
Caucasian
straight or wavy fairly evenly distributed pigment
oval to round shape

39. Hair – 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?
Can DNA individualize a human hair?

40. Hair

41. Hair and DNA
Recent major breakthroughs in DNA profiling have extended this technology to the individualization of human hair.
The probability of detecting DNA in hair roots is more likely for hair being examined in its anagen or early growth phase as opposed to its catagen (middle) or telogen (final) phases.
Often, when hair is forcibly removed a follicular tag, a translucent piece of tissue surrounding the hair’s shaft near the root may be present.
This has proven to be a rich source of nuclear DNA associated with hair.

42. Hair and DNA Mitochondrial DNA can be extracted from the hair shaft.
Mitochondrial DNA is found in cellular material located outside of the nucleus and it is transmitted only from the mother to child.
As a rule, all positive microscopical hair comparisons must be confirmed by DNA analysis.

43. FIBERS: Polymers Long strings of repeating chemical units poly (many)
mer (unit)

44. Fibers: WOOL
Microscopic images of wool fibers

45. Natural Fibers Classified according to their origin
vegetable or cellulose based
animal or protein based
mineral class
asbestos

46. Cellulose Based Fibers
Cotton
Jute
sacks & bags
burlap
backing for tufted carpets & hooked rugs
Oriental rugs
twines & ruff cordage

47. Protein Based Fibers
More vulnerable to environmental degradation than cellulose based fibers
Wool (sheep)
Mohair (goat)
fiber structure similar to wool
half the scales of wool
scales lie flat (smooth surface)
<1% of fibers have a medulla
Silk

48. Natural Fibers Are ... Nonthermoplastic
do not soften when heat is applied
Susceptible to microbial decomposition (mildew & rot)
cellulose based
decomposed by aerobic bacteria & fungi
protein based
decomposed by bacteria and molds
moths, carpet beetles, termites, silverfish

49. Fibers: NYLON
Polarizing microscope image of a nylon fiber.

50. Man-Made Fibers Regenerated Fibers Synthetic Fibers
derived from naturally occurring raw materials that are polymers
rayon
acetate
Synthetic Fibers
made of polymers that do not occur naturally
polyesters
polyamides

51. Man-Made Fibers
Polymers, or macromolecules, are synthetic fibers composed of a large number of atoms arranged in repeating units known as monomers.
The chain-link model of a segment of a polymer molecule. The actual molecule may contain as many as several million monomer units or links.

52. Collection of Fiber Evidence
Investigator must identify & preserve potential fiber “carriers”
Clothing items are packaged individually in paper bags
different items must not be placed on the same surface before being bagged
Tape lifts of exposed skin areas of bodies & inanimate objects
If it is necessary to remove a fiber from an object, the investigator must use clean forceps, place it in a small sheet of paper, fold and label the paper, and place the paper packet inside another container.
Wayne Williams case

53. Analysis of Fiber Evidence
The visible light microspectrophotometer is a way for analysts to compare the colors of fibers through spectral patterns.
More detailed analysis of the fiber’s dye composition can be obtained through a chromatographic separation.
Infrared spectrophotometry is a rapid and reliable method for identifying the generic class of fibers, as does the polarizing microscope.
Depending on the class of fiber, each polarized plane of light will have a characteristic index of refraction.

54. Trace Evidence

55. PAINT
PAINT – Paint chips: become trace evidence when found on clothing or weapons.
Finding chips on weapons at a crime scene may indicate a struggle.
There are 40K different types of paint classified in the database
The leading source of paint chips submitted to crime labs are from hit & run accidents involving automobiles.

56. PAINT and the Automobile ELECTROCOAT PRIMER PRIMER SURFACER
Paint chips originating from an automobile are among the most distinct. This is because the process to finish steal consists of at least four coats.
A manufacturer may use the same paint for thousands of its cars. In order to further determine the origin of a particular chip, lab technicians often analyze the paint binder.
ELECTROCOAT PRIMER
PRIMER SURFACER
BASECOAT
CLEARCOAT

57. Pyrolysis Gas Chromatography
A paint chip is broken down with heat. Once fractionated, the products will give a reading of the makeup of the paint binder. While the paint used on a particular model of car is usually consistent, the binder is often unique. By analyzing the layer structure and the binder, techs can draw conclusions of high certainty, the source of the paint chip.

58. ELECTROCOAT PRIMER
This is the first layer applied to the steel body of a car
This is used to provide corrosion resistance
It is uniform in appearance and thickness
Its color varies from black to grey
Navy Blue Color Coat Paint from a Ford
Navy Blue Color Coat Paint from a Chrysler

59. PRIMER SURFACER
Usually follows the electrocoat primer, and is applied before the basecoat.
The function of this layer is to completely smooth out any seams or imperfections, because the color coat will be applied to this surface.
This layer is highly pigmented
Color pigments are used to minimize color contrast between primer and top coat.

60. BASECOAT ALSO KNOWN AS COLOR COAT
This layer provides the color and aesthetics of the finish, and represents the “eye appeal”
The integrity of this layer depends on its ability to resist weather, UV radiation, and acid rain.
The most common is acrylic base, but the choice of automotive pigments is determined by toxic and environmental concerns.
(The use of lead, chrome, and other heavy metal pigments have been abandoned)

61. CLEAR COAT
An unpigmented clear coat is applied to improve gloss, durability and appearance.
Most are acrylic bases but polyurethane clear coats are increasing in popularity
They provide outstanding etch resistance and appearance.