Trace Evidence – Hair, Fibers and Paint - PowerPoint PPT Presentation

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Trace Evidence – Hair, Fibers and Paint

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  1. Honors Forensic Science Trace Evidence – Hair, Fibers and Paint

  2. I. Hair • A. Not yet possible to individualize a human hair to any single head or body • B. No properties remain consistent • C. Can provide corroborating evidence

  3. D. Morphology • i. Appendage of skin • Ii. Grows from hair follicle • Iii. Shaft of hair • 1. cuticle • 2. cortex • 3. medulla

  4. iv. Cuticle • 1. cuticle is formed by overlapping scales that always point toward tip end of hair • 2. scales are formed from specialized cells that have hardened (keratinized) and flattened • 3. scale pattern not useful for individualization but variety of patterns important for species identification

  5. vi. Medulla • 1. cellular column running through the center of the hair • 2. medullary index = measures the diameter of medulla relative to diameter of the hair shaft • 3. presence and appearance of medulla varies from individual to individual as well as within an individual

  6. 4. Humans • A. Generally have none or fragmented medullas • B. Mongoloid race = continuous medulla

  7. 5. animals. • A. Most have continuous or interrupted medullas

  8. 6. shape • A. Humans – nearly cylindrical in appearance • B. Animals – patterned shape • C. data base s are available

  9. vii. Root • 1. Three phases of hair growth • A. Anagen – initial growth phase during which the hair follicle is actively producing hair • B. Catagen – transition stage between anagen and telogen phases • C. Telogen – final growth phase in which hair naturally falls out of the skin

  10. 2. shape of root depends on phase of hair growth • A. Anagen – follicular tag • B. Catagen – elongated appearance • C. Telogen – club-shaped appearance

  11. II. Identification and Comparison of Hair • A. Generally when dealing with hair evidence, you are either; • i. Trying to determine if human or animal • Ii. Species ID of animal • Iii. If human, does it match hair from a suspect?

  12. b. In comparing hair, criminalist is interested ini.Colorii. lengthiii. Diameteriv. Presence or absence of medullav. Distribution, shape, color of pigment granules in cortex

  13. C. Mainly, hair is class evidence • D. Can use probabilities to tell if 2 hairs came from same individual • E. Can be very useful

  14. f. Can the body area of a hair be determined? • i. Yes, usually without difficulty • Ii. Scalp hair – little diameter variation, uniform distribution of pigment granules • Iii. Pubic hair – short, curly, wide variations in shaft diameter, continuous medulla • Iv. Beard hair – coarse, normally triangular in cross-section, blunt tips

  15. g. Can racial origin of hair be determined? • i. Sometimes • Ii. Caucasian – usually straight or wavy, pigments more evenly distributed, oval in cross-section • Iii. Negroid – curly, dense and unevenly pigmented, oval to flat in shape • Iv. Extreme variation however, so care must be taken

  16. h. Can the age and sex of a person’s hair be determined? • i. Only infant hair can be identified • 1. fine, short in length, fine pigment, rudimentary in character • Ii. No technique to accurately determine sex

  17. i. Is it possible to determine if hair was forcibly removed? • i. Root hair with follicular tissue adhering to it = hair was forcibly removed • Ii. Bulbous shaped root, free of any tissue = hair naturally fell out

  18. j. Are efforts being made to individualize human hair? • i. Can link human hair to a particular individual by characterizing the nuclear DNA present in hair root or in follicular tissue adhering to root • Ii. Can also extract some DNA from hair when in anagen or catagen phase of growth

  19. Iii. Nuclear DNA – DNA present within the nucleus of a cell • 1. inherited from both parents

  20. Iv. Mitochondrial DNA – DNA present in mitochondria located outside cell nucleus • 1. mitochondria supply energy to cell • 2. DNA here is inherited from mother only

  21. III. Collection of hair evidence • A. Questioned hairs must be submitted with adequate numbers of control hairs from victims and suspects • B. Hairs must be collected and submitted from various parts of body (head, pubis, chest, etc.)

  22. IV. Fibers • A. Natural • i. Derived entirely from animal or plant sources • Ii. Wool, mohair, cashmere, fur, cotton

  23. b. Man-made • i. Derived from either natural or synthetic polymers • Ii. Polyesters, nylons, rayons, etc.

  24. Iii. Regenerated • 1. usually raw material of cotton or wood pulp • 2. cellulose extracted, treated, and forced through small holes of spinneret • 3. rayon, acetate, triaceteate

  25. Iv. Synthetic • 1. produced solely from synthetic chemicals • 2. nylons, polyesters, acrylics • 3. became reality when scientists developed method of synthesizing polymers

  26. A. Polymer = substance composed of a large number of atoms; atoms are usually arranged in repeating units called monomers

  27. B. Polymer is basic chemical substance of all synthetic fibers • C. Often called macromolecules • D. Can change basic structure of molecules and how they are linked together to change properties of polymer

  28. c. Identification and Comparison of Fibers • i. Man-made fibers • 1. evidential value is related to ability to trace origin • 2. most often is comparative in nature • 3. compare color and diameter • 4. also compare lengthwise striations on surface, pitting of surface, shape

  29. 5. need to compare dye composition also • 6. use chromatography to separate dye constitutents • 7. chemical composition • 8. often have crystalline properties so can measure birefringence

  30. 9. Light passing through fiber is polarized so will have characteristic index of refraction • 10. infrared spectrophotometry to identify class or sub-class of fiber • 11. In the end, it is still class evidence

  31. d. Collection of Fiber Evidence • i. Can easily be overlooked • Ii. Have to identify and collect possible carriers of fiber evidence • Iii. Care taken to avoid loss of evidence or contamination

  32. V. Paint • A. Commonly encountered form of evidence • B. Found often in hit and run and burglary cases • C. Compare paint chips to determine common origin • D. Also can assist in identifying color, make and model of automobiles

  33. e. What is Paint? • i. Paint = pigments, additives and binder all dissolved or dispersed in a suitable solvent • Ii. Pigments • 1. impart color and opacity • 2. usually mixtures of different organic and inorganic compounds

  34. Iii. Binder • 1. provides support medium for pigments and additives • 2. polymeric substance

  35. f. Automotive finishing system • i. Electrocoat primer • 1. provides corrosion resistance • 2. color ranges from gray to black

  36. Ii. Primer surface • 1. corrosion control and smooth out finish • 2. epoxy-modified polyesters • 3. highly pigmented; match with topcoat

  37. Iii. Basecoat • 1. provides color and aesthetics to finish • 2. binder system = acrylic – based polymer • 3. different pigments added

  38. Iv. Clear-coat • 1. un-pigmented • 2. improve gloss, durability and appearance • 3. acrylic based or polyurethane