Trace Evidence HAIR, FIBERS & PAINT

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.

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.

Morphology of Hair

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.

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.

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

Cuticle Scale patterns can be used for species ID

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.

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.

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

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.

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)

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?

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.

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.

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.

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

Matching Hairs ID w/ Comparison Microscope

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

Forcibly Removed Hair from the scalp Stretches and Damages the Root

Forcibly Removed Hairs MAY have tissue attached.

ANIMAL: Muskrat Hair

ANIMAL: Deer Hair

HUMAN: Head Hair (razor-cut)

HUMAN: Head Hair (split)

HUMAN: Head Hair (cut tip)

HUMAN: Pubic Hair

HUMAN: Caucasian or European Hair

HUMAN: Mongoloid or Asian Hair

HUMAN: Negroid or African Hair

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

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.

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.

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

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

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.

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

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?

Hair

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.

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.

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

Fibers: WOOL Microscopic images of wool fibers

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

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

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

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

Fibers: NYLON Polarizing microscope image of a nylon fiber.

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

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.

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

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.

Trace Evidence

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.

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

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. http://www.shu.ac.uk/schools/sci/chem/tutorials/chrom/gaschrm.htm

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

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.

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)

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.