Hairs, Fibers, and Paint

Hairs, Fibers, and Paint Criminalistics Chapter 8

Hair • A good indicator of individual identity • Resistant to chemical decomposition • Retains structural features over time • Hair is not an absolute indicator of identity but can be a good indicator of identity

Morphology of Hair • Appendage of the skin that grows out of a hair follicle • Begins at the hair root embedded in the follicle and extends outward into the shaft and ends at the tip • The hair shaft is most commonly tested by forensic scientists

The Hair Shaft: 4 Parts Coronal “Crown Shaped” Scales • The cuticle: outside covering of hair • Covered in scales that point toward the tip • Scales are used in identification of the hair • Animal V. Human Hair Imbricate “Flattened” Scales Spinous “Spiny” Scales

Cuticle Photographs The cuticle is a translucent outer layer of the hair shaft consisting of scales that cover the shaft. This photograph illustrates how the cuticular scales always point from the proximal or root end of the hair to the distal or tip end of the hair.

Cuticle Photographs Spinous or petal-like scales are triangular in shape and protrude from the hair shaft. They are found at the proximal region of mink hairs and on the fur hairs of seals, cats, and some other animals. They are never found in human hairs. • Photomicrograph of the proximal scale pattern in mink hairs. The imbricate or flattened scales type consists of overlapping scales with narrow margins. They are commonly found in human hairs and many animal hairs.

The Hair Shaft: 4 Parts • The cortex: inside the protective layer of cuticle • Made of cells that are aligned parallel to the length of the hair • Pigment granules that provide color are found in the cortex

The Hair Shaft: 4 Parts • The medulla: found in the center of the hair • Predominant feature of hair • Can be continuous, interrupted, or fragmented • Can be different shapes in cross-section and can be searched using a database

Medulla Examples In human hairs, the medulla is generally amorphous in appearance, whereas in animal hairs, its structure is frequently very regular and well defined. Photomicrograph of Uniserial Ladder Medulla Photomicrograph of Multiserial Ladder Medulla The above examples have a well-defined appearance and came from a rabbit.

Medulla Examples Photomicrograph of Animal Hair with vacuolated medullae. Photomicrograph of Deer Medulla with lattice-shaped medulla.

Human Medulla Examples When the medulla is present in human hairs, its structure can be described as—fragmentary or trace, discontinuous or broken, or continuous. This figure is a diagram depicting the three basic medullary types. Discontinuous Medulla in Human Hair

Hair Identification Animal Versus Human Hairs • Human hairs are distinguishable from hairs of other mammals. Animal hairs are classified into the following three basic types. • Guard hairs that form the outer coat of an animal and provide protectionFur or wool hairs that form the inner coat of an animal and provide insulationTactile hairs (whiskers) that are found on the head of animals provide sensory functions

Hair Identification Animal Versus Human Hairs Human hairs are generally consistent in color and pigmentation throughout the length of the hair shaft, whereas animal hairs may exhibit radical color changes in a short distance, called banding. The medulla, when present in human hairs, is amorphous in appearance, and the width is generally less than one-third the overall diameter of the hair shaft. The medulla in animal hairs is normally continuous and structured and generally occupies an area of greater than one-third the overall diameter of the hair shaft.

The Hair Shaft: 4 Parts • The root: provides for growth of old and new hair • Three phases of hair growth: • Anagen (up to 6 yrs): root attached to follicle for continued growth; root bulb is flame-shaped • Catagen (2-3 weeks): slowed growth; root bulb has an elongated appearance • Telogen (2-6 months): hair growth ends and is shed; root bulb is club-shaped

Phases of Root Growth Flame-Shaped Root Elongated Root Club-Shaped Root

Identification and Comparison of Hair • Most comparisons are human v. animal • Human-human comparisons are problematic • Variable morphological characteristics • Vary from person to person • Vary within a single individual

Hair Comparison • Use a comparison microscope • Compare with standard/reference samples • Try to match color, length, and diameter • Can determine dyed or bleached hair from natural • Time since coloring can be determined because hair grows ~1cm per month

Hair Comparison Pigment granules are small, dark, and solid structures that are granular in appearance. They vary in color, size, and distribution in a single hair. In humans, pigment granules are commonly distributed toward the cuticle as shown in Figure 1, except in red-haired individuals as in Figure 2. Animal hairs have the pigment granules commonly distributed toward the medulla, as shown in Figure 3. Figure 1 Figure 2 Figure 3

Human Hair Identification Human hair can be identified by racial origin, body area and other classifying techniques. Key characteristics serve as racial indicators. These indicators are generalities and apply primarily to head hairs. The examiner may encounter hairs that cannot easily be associated with a particular racial model because of poorly defined characteristics, limited size, or inconsistent indicators. These hairs can be identified as apparent racial mixtures or as not classifiable.

Caucasian Hair Identification • Shaft diameter: moderate with minimal variation (mean diameter for human head hairs - 80um) Pigment granules: sparse to moderately dense with fairly even distribution Cross-sectional shape: oval • Photomicrograph of Caucasian Head Hair Photomicrograph of Cross-section of Caucasian Hair

Negroid Hair Identification • Shaft diameter: moderate to fine with considerable variationPigment granules: densely distributed (hair shaft may be opaque) and arranged in prominent clumps Shaft: prominent twist and curl Cross-sectional shape: flattened • Photomicrograph of Negroid Head Hair • Photomicrograph of Cross-section of Negroid Hair

Mongoloid Hair Identification • Shaft diameter: coarse and usually with little or no variation Pigment granules: densely distributed and often arranged in large patchy areas or streaks Medulla: prominent (often broad and continuous) Cuticle: thick Cross-sectional shape: round Photomicrograph of Mongoloid Head Hair • Photomicrograph of Cross-section of Mongoloid Hair

Hair Comparison • Highly subjective comparative test • DNA analysis of hair is a much more reliable testing technique

Individualizing Human Hair • Nuclear DNA Analysis: • DNA found in the nucleus of the cell • Must have follicular tag or root structure present to test

Individualizing Human Hair • Mitochondrial DNA Analysis: • DNA found in cellular material outside of the nucleus • Can be tested without follicle or root structure • More copies of mitochondrial DNA in cells

Collection and PreservationOf Hair Evidence • Must be submitted with an adequate sample of hair from the victim of a crime, those entering a crime scene, or a suspect • Hair samples must be obtained from the same parts of the body • Usually involve head or pubic hair

Collection and PreservationOf Hair Evidence • Head hair: approximately 50 full-length hairs needed • Pubic hair: approximately 25 hairs needed • In rape cases, area must be combed for hair transfer and then packaged in a separate envelope

Collection and PreservationOf Hair Evidence • Hair must be pulled out of the skin or by clipping it at the skin line • Hair is collected from the victims of suspicious deaths at autopsy

Fibers • Comprise our fabrics and garments • Important evidence in incidences that involve personal contact Homicides, assaults, & sexual offenses Can also be transferred in hit-and-run cases

Problems with Fiber Analysis • Mass production of garments and fabrics has limited finding origin points • It is very unusual to identify fiber evidence with a high degree of certainty

Natural Fibers • Derived in whole from animal or plant sources • Animal sources: sheep, goats, camels, llamas, alpacas, mink, rabbit, beaver, and muskrat • Plant sources: primary source Cotton Wool Fibers Cotton Fibers

Cross-Sectional Patterns of Man-Made Fibers Man-Made Fibers • Derived from either natural or synthetic polymers • Most have distinguishable cross-sectional patterns • Examples: Rayon, Nylon, Acrylic, Polyester, and Spandex

Identification and Comparison of Man-Made Fibers • Microscopic comparison using a comparison microscope • Color and Diameter • Striations and Pitting • Shape of Fiber in Cross-Section

Identification and Comparison of Man-Made Fibers • Dye comparison using a microspectrophotometer • Not limited by size of sample

Identification and Comparison of Man-Made Fibers • Chromatography • Separate shades of color on a chromatograph

Identification and Comparison of Man-Made Fibers • Test chemical composition • Fibers are separated into classes • Light Analysis • Light passing through a fiber will be polarized and have a specific index of refraction • Refraction indexes can be compared

Problems with Fiber ID • Fiber strands cannot be linked with any certainty to any single garment or origin • Due to mass production of clothing, carpets, and other fiber sources

Importance of Fiber Evidence • Circumstances of the case • Other evidence that may link the suspect to the scene • Location, number, and nature of fibers examined • Judgment of the experienced examiner

Collection and Preservation of Fiber Evidence • Fiber evidence often cannot be seen with the naked eye • Fiber evidence can be associated with any type of crime and items must be packaged separately

Packaging of Fiber Evidence • Articles of clothing must be packaged separately in paper bags • Carpets, rugs, and bedding must be folded carefully to preserve fiber evidence • Car seats must be covered in plastic sheets • Knife blades should be covered to protect fibers that may be stuck to them

Packaging of Fiber Evidence • If fibers are to be removed from evidence before it goes to the lab: • The possibility exists that the evidence would be lost in moving it from the crime scene • Clean forceps must be used and the evidence double enveloped.

Paint Evidence • Used in hit-and-run and burglary cases • Often two or more samples are examined to determine a common origin

Automobile Paint Layering • First Layer: Electrocoat Primer • Provides corrosion resistance to steel • Second Layer: Primer Surfacer • Hides any seams or imperfections in the automobile’s body • Third Layer: Basecoat • Color of the automobile • Fourth Layer: Clearcoat • Improves gloss, durability, and appearance

Examination of Paint • Basecoat (color layer) provides the most evidence because of paint chemical composition • Layering of paint also helps forensic scientists determine a common point of origin

Value of Paint Examination • Chemical composition of different paints can be linked to different makes and models of automobiles and can assist in locating a suspect vehicle

Collection and Preservation of Paint Evidence • Loose paint chips can be picked up with forceps and placed in envelopes or tight-lid containers • Reference samples must be taken in an area adjacent to the missing paint chip by using a scalpel or razor blade

Hairs, Fibers, and Paint