Ch 8 – Hairs, Fibers, and Paint

Trace Evidence
HAIR, FIBERS & PAINT
1
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.
2
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.
3
Morphology of Hair
4
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.
5
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.
6
Cuticle

Formed by overlapping
scales
 points toward tip of
hair
 specialized
keratinized cells
(hardened)
 Paint on pencil
7
Cuticle

Scale patterns
can be used
for species ID
8
Cortex
The main body of the
hair shaft.



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
9
Wood of pencil
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 the10
species.
Medulla


A collection of cells
appearing like a
central canal
Medullary Index


comparison of medulla
diameter to shaft
diameter
Graphite in pencil
11
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.
12
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)
13
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?
14
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.
15
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.

16
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.
17
HAIR
Hairs indicating forced (left) and natural
(right) removal.
18
Matching Hairs ID w/
Comparison Microscope
19
Naturally Shed Hairs, i.e.,
Combing: Undamaged Roots, club-shaped
20
Forcibly Removed Hair from the scalp
Stretches and Damages the Root
21
Forcibly Removed Hairs
MAY have tissue attached.
Tissue
22
ANIMAL: Muskrat Hair
23
ANIMAL: Deer Hair
24
HUMAN: Head Hair
(razor-cut)
25
HUMAN: Head Hair (split)
26
HUMAN: Head Hair
(cut tip)
27
HUMAN: Pubic Hair
28
HUMAN: Caucasian
or European Hair
29
HUMAN: Mongoloid or
Asian Hair
30
HUMAN: Negroid or
African Hair
31
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
32
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.
33
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.
34
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
35
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

36
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.
37
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
38
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?
39
 Can DNA individualize a human hair?

Hair
40
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.
41
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.
42
FIBERS: Polymers
Long strings of repeating chemical units
 poly (many)
 mer (unit)
43
Fibers: WOOL
Microscopic images of wool fibers
44
Natural Fibers

Classified according to their origin
vegetable or cellulose based
 animal or protein based
 mineral class

 asbestos
45
Cellulose Based Fibers
Cotton
 Jute


sacks & bags
 burlap

backing for tufted carpets & hooked rugs
 Oriental

rugs
twines & ruff cordage
46
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
47
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
48
Fibers: NYLON
Polarizing microscope image of a nylon fiber.
49
Man-Made Fibers

Regenerated Fibers


derived from naturally occurring raw materials
that are polymers
 rayon
 acetate
Synthetic Fibers

made of polymers that do not occur naturally
 polyesters
 polyamides
50
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.
51
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
52
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.
53
Trace Evidence
54
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.
55
PAINT and the
Automobile
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.
56
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.
57
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
58
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.
59
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)
60
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.
61
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