Forensics:hair, fiber, and paints

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  • I'm a forensic hair examiner and I applaud your images, they're great! May I use 2 of them please in future presentations (with acknowldgement of source). Thanks SRT
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  • this is great!! Congratulations, i found your presentation very useful in my class forensic chemistry, can i copy this? thank you..and more power.
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Forensics:hair, fiber, and paints

  1. 1. Hairs, Fibers, and Paint Chapter 8
  2. 2. Dermis <ul><li>Contains </li></ul><ul><ul><li>smooth muscle </li></ul></ul><ul><ul><li>blood vessels </li></ul></ul><ul><ul><li>nerve tissue </li></ul></ul><ul><ul><li>hair follicles (accessory organ of skin) </li></ul></ul><ul><ul><li>sweat glands (accessory organ of skin) </li></ul></ul><ul><ul><li>sebaceous glands (accessory organ of skin) </li></ul></ul><ul><li>Contains nerve receptors – to sense light/heavy touch or pressure </li></ul><ul><li>Contains connective tissue made of collagen and elastic fibers </li></ul>
  3. 3. Full-thickness Skin
  4. 4. Accessory Organs of the Skin <ul><li>Hair follicles </li></ul><ul><li>Nails </li></ul><ul><li>Skin glands </li></ul><ul><ul><li>Sebaceous glands </li></ul></ul><ul><ul><li>Sweat glands (a.k.a sudoriferous glands) </li></ul></ul><ul><ul><ul><li>Eccrine </li></ul></ul></ul><ul><ul><ul><li>Apocrine </li></ul></ul></ul>
  5. 5. Hair Follicles <ul><li>Follicles are present on all skin excepts palms, soles, lips, nipples </li></ul><ul><li>In some areas that grow hair, the hair may be fine, while in others it may be thick </li></ul><ul><li>A hair grows out of a deep tube that extends from the surface of the skin, all the way into the dermal layer – this is a follicle </li></ul><ul><li>Each hair follicle is also connected to sebaceous glands that produce oils and other secretions </li></ul>
  6. 6. Hair Follicle, cont’d. <ul><li>The follicle contains the growing hair shaft </li></ul><ul><li>The base of the hair is composed of actively dividing epidermal cells </li></ul><ul><li>These epidermal cells are nourished by dermal blood vessels near the hair base – this area at the base of the hair follicle is called the hair papilla </li></ul>
  7. 7. Morphology and Structure of Hair
  8. 8. Hair Morphology Con’t
  9. 9. Morphology: Cuticle <ul><li>Protective coating made of overlapping scales, produce a characteristic pattern </li></ul><ul><li>Scales always point toward tip of hair </li></ul><ul><li>Not useful in individualizing human hair </li></ul><ul><li>Can be used for species identification </li></ul>
  10. 11. Morphology: Cortex <ul><li>Embedded with pigment granules that give hair its color </li></ul><ul><li>The color, shape and distribution of the granules provide points for forensic comparison </li></ul>
  11. 12. Morphology: Medulla <ul><li>canal like structure of cells that runs through the center of the cortex </li></ul>
  12. 13. Medullary Index <ul><li>Measure of the diameter of the medulla relative to the diameter of the hair shaft </li></ul><ul><li>Usually expressed as a fraction </li></ul><ul><li>Humans: medullary index < 1/3 </li></ul><ul><li>Animals: medullary index > 1/2 </li></ul>
  13. 14. Medullary Index: How to figure it out…
  14. 15. Medulla of Different Species
  15. 16. Medulla Patterns <ul><li>Uniserial -small blocks in a row </li></ul><ul><li>Multiserial - several rows of blocks across a hair diameter </li></ul>
  16. 17. <ul><li>Vacuolated – Uneven pattern </li></ul><ul><li>Lattice -circular pattern </li></ul>
  17. 18. Forensic Analysis of Medulla <ul><li>Presence of medulla varies quite a bit: even hair to hair </li></ul><ul><li>Human head hairs generally have no medulla or may be fragmented ones; except Mongoloid race whose medulla is usually continuous </li></ul><ul><li>Most animals have medulla that is continuous or interrupted </li></ul><ul><li>The shape of the medulla can help identify a species </li></ul><ul><li>Examples: </li></ul><ul><ul><ul><li>Most animals and humans: cylindrical </li></ul></ul></ul><ul><ul><ul><li>Cats: pearl shape </li></ul></ul></ul><ul><ul><ul><li>Deer: spherical occupying whole hair shaft </li></ul></ul></ul>
  18. 19. Identification and Comparison of Hair <ul><li>Morphological Characteristics do not allow individualization of a human hair to any single head or body </li></ul><ul><li>Hair when collected with an adequate number of standards/references can provide strong circumstantial evidence </li></ul><ul><li>Scale structure, medullary index, and medullary shape are most often used for hair comparison </li></ul><ul><li>Evidential value lies with degree of probability associated with a questioned hair and an particular individual </li></ul><ul><li>11 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 </li></ul>
  19. 20. Morphology: Root <ul><li>Human hair grows in three developmental stages: anagen, catagen, and telogen phases </li></ul>
  20. 21. Root: Anagen Phase <ul><li>Initial growth phase during which hair follicle is actively producing hair, phase may last 6 years, root is flame like in appearance </li></ul><ul><li>When pulled this root may contain a follicular tag (rich source of DNA) </li></ul>Anagen hair root Root w/ follicular tag
  21. 22. Root: Catagen Phase <ul><li>A 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 follicle </li></ul>Catagen hair root
  22. 23. Root: Telogen phase <ul><li>Hair growth has ended—root takes on a club-like appearance, the hair will be pushed out of the follicle causing the hair to shed naturally </li></ul>Telogen hair root
  23. 25. Types of hair: curly vs. straight
  24. 26. Hair in the anagen phase Electronmicrograph showing new hairs emerging from the hair follicles of the scalp
  25. 27. Telogen phase showing the “clubed” appearance
  26. 28. Appearance of the root of pulled human hair
  27. 29. <ul><li>Razor cut tip of hair: Blunt cut tip of hair: </li></ul>
  28. 30. Split hair tips
  29. 31. Fragments and debris on hair
  30. 32. Lice- nits (egg cases on hair shaft)
  31. 33. Matching hair using a comparison microscope
  32. 34. Important Forensic Questions <ul><li>Can the body area from which a hair originated be determined? </li></ul><ul><li>Can the racial origin of hair be determined? </li></ul><ul><li>Can the age and sex of an individual be determined from a hair sample? </li></ul><ul><li>Is it possible to determine if a hair was forcibly removed from the body? </li></ul><ul><li>Are efforts being made to individualize human hair? </li></ul><ul><li>Can DNA individualize a human hair? </li></ul><ul><li>Define nuclear and mitochondrial DNA—note similarities and differences </li></ul><ul><li>Find answers in text pgs 201 - 204 </li></ul>
  33. 35. Fibers: Natural <ul><li>Derived entirely from animal or plant sources </li></ul><ul><li>Most prevalent plant fiber is cotton. </li></ul><ul><li>Its widespread use has made its evidential value almost meaningless </li></ul><ul><li>Cotton has a ribbon-like shape with twists at regular intervals </li></ul><ul><li>Animal sources include sheep (wool), goats (mohair, cashmere) and many other sources </li></ul>
  34. 36. Man-Made Fibers <ul><li>Fibers derived from either natural or synthetic polymers </li></ul><ul><li>The fibers are made by forcing polymeric material through the holes of a spinneret </li></ul><ul><li>Rayon and then nylon were the first two man-made fibers (year 1911) </li></ul>
  35. 37. Man-Made Fibers Con’t <ul><li>Regenerated Fibers </li></ul><ul><ul><li>Made from regenerated cellulose (wood or cotton pulp) </li></ul></ul><ul><ul><li>Include such fibers as rayon, acetate, and triacetate </li></ul></ul><ul><li>Synthetic Fibers </li></ul><ul><ul><li>Currently manufactured </li></ul></ul><ul><ul><li>Made from synthetic chemicals called polymers </li></ul></ul><ul><ul><li>Include such fibers as nylons, polyesters, and acrylics </li></ul></ul>
  36. 38. Polymers <ul><li>Basic chemical substance of all synthetic fibers </li></ul><ul><li>Consist of long chains of repeating molecules. The repeating molecular units in the polymer are called monomers. </li></ul><ul><li>Often referred as macromolecules or “big” molecules </li></ul><ul><li>Countless varieties exist </li></ul>
  37. 39. ID and Comparison of Man-Made Fibers <ul><li>Fabrics that can be fitted together at their torn edge are easy to match </li></ul><ul><li>Microscopic comparison of color and diameter </li></ul><ul><li>Comparison of lengthwise striations and pitting on the surface of a fiber </li></ul><ul><li>The shape of the fiber—ex. Wayne Williams case </li></ul><ul><li>Note: 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 </li></ul>
  38. 40. Tools and Techniques to Aid in Comparing Fibers <ul><li>Light infrared spectrophotometer—compares colors and chemical composition through spectral patterns </li></ul><ul><li>Chromatography—compares dye composition </li></ul><ul><li>Refraction—ID’s fiber by refractive index </li></ul><ul><li>Comparison microscope—reveals shape, coloring, pitting and striations </li></ul>
  39. 41. Forensic Examination of Paint <ul><li>Paint evidence is frequently encountered in hit-and-run and burglary cases </li></ul><ul><li>Most examinations consist in comparing two or more paints to establish their origin </li></ul><ul><li>Often color, make and model of a vehicle can be determined </li></ul>
  40. 42. Paint Characteristics <ul><li>Paint spread on a surface will dry into a hard film consisting of pigments and additives suspended in a binder </li></ul><ul><li>The binder provides the support medium for the pigments and additives. </li></ul><ul><li>Modern automotive finishing consists of at least four coatings: </li></ul><ul><li>Electrocoat Primer : first layer, electroplated to the car—provides corrosion resistance—color from black to grey </li></ul><ul><li>Primer Surface : second layer, smoothes out and hides any seams on the car—color pigments are used to minimize contrast between primer and topcoats </li></ul><ul><li>Basecoat: third layer, provides the basic color and appearance to the car </li></ul><ul><li>Clearcoat: final coat, provides great appearance (glossiness) and protection for the car </li></ul>
  41. 43. Tools and Techniques to Aid in Paint Examination <ul><li>Questioned and known specimens are compared side by side under a stereomicroscope for color, surface texture, and color layer sequence </li></ul><ul><li>Note: Layer sequence is very important evidence: forensic scientists will try to match layers with respect to number and sequence of color </li></ul><ul><li>Note: Layer structure alone will not provide enough information to be individualized to a single source </li></ul><ul><li>Chemical analysis of the paint’s pigments and binder composition provides further points of comparison. </li></ul><ul><li>Typically, gas chromatography is used to determine the chemical make-up of the binder material. </li></ul><ul><li>Infrared spectrophotometry is also used to determine the binder composition of paint. </li></ul><ul><li>Elements of the paint pigments can be identified with a number of techniques, including spectroscopy, neutron activation analysis, and x-ray diffraction </li></ul><ul><li>Using these techniques the odds against crime-scene paint originating from another randomly chosen vehicle is approximately 33,000 to one. </li></ul>

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