Trace Evidence

HAIR, FIBERS & PAINT

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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.

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Morphology of Hair

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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.

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Cuticle

Formed by overlapping scales points toward tip of

hair specialized

keratinized cells (hardened)

Paint on pencil

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Cuticle

Scale patterns can be used for species ID

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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 9

The main body of the hair shaft.

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. 10

Medulla

A collection of cells appearing like a central canal

Medullary Index comparison of medulla

diameter to shaft diameter

Graphite in pencil

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Medulla Patterns

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• 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.

The medulla may be continuous, interrupted, fragmented, or absent.

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)

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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?

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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.

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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.

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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.

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HAIR

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

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Matching Hairs ID w/Comparison Microscope

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

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Forcibly Removed Hair from the scalp Stretches and Damages the Root

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Forcibly Removed HairsMAY have tissue attached.

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Tissue

ANIMAL: Muskrat Hair

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ANIMAL: Deer Hair

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HUMAN: Head Hair (razor-cut)

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HUMAN: Head Hair (split)

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HUMAN: Head Hair (cut tip)

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HUMAN: Pubic Hair

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HUMAN: Caucasian or European Hair

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HUMAN: Mongoloid or Asian Hair

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HUMAN: Negroid or African Hair

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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

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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.

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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.

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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

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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

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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.

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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

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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? 39

Hair

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Hair and DNA

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• 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.

Hair and DNA

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• 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.

FIBERS: Polymers

Long strings of repeating chemical units poly (many) mer (unit)

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Fibers: WOOL

Microscopic images of wool fibers44

Natural Fibers

Classified according to their origin vegetable or cellulose based animal or protein based mineral class

asbestos

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Cellulose Based Fibers

Cotton Jute

sacks & bags burlap

backing for tufted carpets & hooked rugs Oriental rugs

twines & ruff cordage

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Protein Based Fibers

More vulnerable to environmental degradation than cellulose based fibers

Wool (sheep) Mohair (goat)

fiber structure similar to woolhalf the scales of woolscales lie flat (smooth surface)<1% of fibers have a medulla

Silk47

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

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Fibers: NYLON

Polarizing microscope image of a nylon fiber.49

Man-Made Fibers

Regenerated Fibers derived from naturally occurring raw materials

that are polymersrayonacetate

Synthetic Fibers made of polymers that do not occur naturally

polyesterspolyamides

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Man-Made Fibers

Polymers, or macromolecules, are synthetic fibers composed of a large number of atoms arranged in repeating units known as monomers.

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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.

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 case52

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.

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Trace Evidence

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PPAAIINNTT 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

PPAAIINNTT and the

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.

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Automobile

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

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Navy Blue Color Coat

Paint from a Ford

Navy Blue Color Coat Paint from a Chrysler

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.

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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)

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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.

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