4 Morphology: CuticleProtective coating made of overlapping scales, produce a characteristic patternScales always point toward tip of hairNot useful in individualizing human hairCan be used for species identification
6 Morphology: CortexMade of spindle-shaped cells aligned in a regular array, parallel to the length of the hairEmbedded with pigment granules that give hair its colorThe color, shape and distribution of the granules provide points for forensic comparison
7 Morphology: Medullacanal like structure of cells that runs through the center of the cortex
8 Medullary IndexMeasure of the diameter of the medulla relative to the diameter of the hair shaftUsually expressed as a fractionHumans: medullary index < 1/3Animals: medullary index > 1/2
10 Forensic Analysis of Medulla Presence of medulla varies quite a bit: even hair to hairHuman head hairs generally have no medulla or may be fragmented ones; except Mongoloid race whose medulla is usually continuousMost animals have medulla that is continuous or interruptedThe shape of the medulla can help identify a speciesExamples:Most animals and humans: cylindricalCats: pearl shapeDeer: spherical occupying whole hair shaft
11 Identification and Comparison of Hair Morphological hair characteristics do not yet allow individualization of a human hair to any single sourceHair when collected with an adequate number of standards/references can provide strong circumstantial evidenceScale structure, medullary index, and medullary shape are most often used for hair comparisonEvidential value lies with degree of probability associated with a questioned hair and an particular individual11 percent of all morphological hair matches are generally found to be non-matches—meaning microscopic hair comparisons are presumptive in nature—must be confirmed by DNA comparisons
12 Morphology: RootHuman hair grows in three developmental stages: anagen, catagen, and telogen phases
13 Root: Anagen PhaseInitial growth phase during which hair follicle is actively producing hair, phase may last 6 years, root is flame like in appearanceWhen pulled this root may contain a follicular tag (rich source of DNA)Anagen hair rootRoot w/ follicular tag
14 Root: Catagen PhaseA transition phase—hair grows at a decreasing rate for two to three weeks—elongated appearance as root bulb shrinks and is being pushed out of hair follicleCatagen hair root
15 Root: Telogen phaseHair growth has ended—root takes on a club-like appearance—during two-six month period, the hair will be pushed out of the follicle causing the hair to shed naturallyTelogen hair root
16 Important Forensic 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?
17 Fibers: NaturalDerived entirely from animal or plant sources Most prevalent plant fiber is cotton.Its widespread use has made its evidential value almost meaninglessCotton has a ribbon-like shape with twists at regular intervalsAnimal sources include sheep (wool), goats (mohair, cashmere) and others
18 Man-Made FibersFibers derived from either natural or synthetic polymersThe fibers are made by forcing polymeric material through the holes of a spinneretRayon and then nylon were the first two man-made fibers (year 1911)
19 Man-Made Fibers Con’t Regenerated Fibers Synthetic Fibers Made from regenerated cellulose (wood or cotton pulp)Include such fibers as rayon, acetate, and triacetateSynthetic FibersCurrently manufacturedMade from synthetic chemicals called polymersInclude such fibers as nylons, polyesters, and acrylics
20 Polymers Basic chemical substance of all synthetic fibers Consist of long chains of repeating molecules. The repeating molecular units in the polymer are called monomers.Often referred as macromolecules or “big” moleculesCountless varieties exist
21 ID and Comparison of Man-Made Fibers Fabrics that can be fitted together at their torn edge are easy to matchMicroscopic comparison of color and diameterComparison of lengthwise striations and pitting on the surface of a fiberThe shape of the fiber—ex. Wayne Williams caseNote: Combined factors of color, size, shape, microscopic appearance, chemical composition, and dye content make it very unlikely to find two different people wearing identical fabrics
22 Tools and Techniques to Aid in Comparing Fibers Light infrared spectrophotometer—compares colors and chemical composition through spectral patternsChromatography—compares dye compositionRefraction—ID’s fiber by refractive indexComparison microscope—reveals shape, coloring, pitting and striations
23 Forensic Examination of Paint Paint evidence is frequently encountered in hit-and-run and burglary casesMost examinations consist in comparing two or more paints to establish their originOften color, make and model of a vehicle can be determined
24 Paint Characteristics Paint spread on a surface will dry into a hard film consisting of pigments and additives suspended in a binderThe binder provides the support medium for the pigments and additives.
25 Paint Characteristics Modern automotive finishing consists of at least four coatings:Electrocoat Primer: first layer, electroplated to the car—provides corrosion resistance—color from black to greyPrimer Surface: second layer, smoothes out and hides any seams on the car—color pigments are used to minimize contrast between primer and topcoatsBasecoat: third layer, provides the basic color and appearance of the carClearcoat: final coat, provides great appearance (glossiness) and protection for the car
26 Techniques to Aid in Paint Examination Questioned (L) and known (R) specimens are compared side by side under a stereomicroscope for color, surface texture, and color layer sequence*Note: Layer sequence is very important evidence: forensic scientists will try to match layers with respect to number and sequence of color*Note: Layer structure alone will not provide enough information to be individualized to a single sourceChemical analysis of the paint’s pigments and binder composition provides further points of comparison.
27 Tools to Aid in Paint Examination Gas chromatography is used to determine the chemical make-up of the binder material.Infrared spectrophotometry is also used to determine the binder composition of paint.Elements of the paint pigments can be identified with a number of techniques, including spectroscopy, neutron activation analysis, and x-ray diffractionUsing these techniques the odds against crime-scene paint originating from another randomly chosen vehicle is approximately 33,000 to one.