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Fiber And Hair Evidence
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Fiber And Hair Evidence

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Fiber And Hair Evidence Fiber And Hair Evidence Presentation Transcript

  • Fiber and Hair Evidence
  • Fibers
    • most often used as class evidence
    • can provide strong corroborating evidence to place perpetrator at crime scene
  • Fibers
    • fiber
      • many filaments twisted or bonded together to form thread or yarn
    • filament
      • single strand of material of indefinite length
  • Fibers
    • can be natural
      • silk, wool, mohair, cashmere, angora, cotton, linen, jute, sisal, hemp, ramie, asbestos, fiberglass, rayon
    • can be artificial or synthetic
      • acrylic, aramid, nylon, olefin, spandex, polyester, modacrylic
  • Fibers
    • physical properties
      • color
        • chromatography of dyes
        • polarization with light
      • blend and /or weave
      • diameter of fibers
      • cross sectional shape
  •  
  • Fibers
    • physical properties
      • # of filaments
      • density
      • refractive index
        • refraction is the bending of light waves due to a change in the velocity
      • fluorescence
  • Fibers
    • chemical properties
      • burning tests (oxidation) analysis
        • ash, behavior in and out of flame, odor
      • thermal decomposition
        • pH, residue and component chemicals
      • chemical decomposition
        • treatment with various strong acids, bases and solvents
  • Fibers
    • many of these tests would be made between the unknown and
      • reference samples taken at scene
      • reference samples taken from individuals involved at scene
      • exemplars – scientific standards accepted widely
        • usually found in databases
  • Fibers
    • many of these tests would be made between the unknown &
      • reference samples taken at scene
      • reference samples taken from individuals involved at scene
      • exemplars – scientific standards accepted widely
        • usually found in databases
  • Hair
    • considered a type of fiber
    • not able to individualize unless DNA is present
    • w/o DNA, it can provide strong corroborative evidence for placing an individual at a crime scene
  • Hair
    • morphology
      • root
        • in follicle
      • shaft
        • cuticle
        • cortex
        • medulla
      • tip/end
  • Hair
    • morphology
      • root
        • in follicle
      • shaft
        • cuticle
        • cortex
        • medulla
      • tip/end
  • Hair
    • morphology - shaft
      • cuticle
        • scale structure covering the exterior of the hair
        • scales always point to tip of hair
        • scale pattern often used for species identification
  • Hair
    • morphology - shaft
      • cortex
        • main body of the hair shaft
        • pigment giving hair its color is embedded in the cortex
          • lack of pigment = gray or white
          • number, shape and distribution of pigment granules can be used to narrow down class
  • Hair
    • morphology - shaft
      • medulla
        • may appear dark or translucent depending on substances inside
        • can be continuous, interrupted or fragmented
        • also used to identify to species
      • medullary index
        • measures diameter of medulla relative to diameter of hair shaft
        • humans usu. less than 1/3, animals usu. more than ½
  • Hair
    • morphology - root
      • located in hair follicle of skin
      • three stages of growth
        • anagen phase: major growth
        • catagen phase: intermediate
        • telogen phase: mature hair – will “fall” out
  • Hair
    • morphology - root
      • telogen
        • naturally shed hairs, such as a head hair dislodged through combing, display undamaged, club-shaped roots
  • Hair
    • morphology - root
      • anagen or catagen
        • a hair forcibly removed from the scalp will exhibit stretching and damage to the root area
        • forcibly removed hairs may have tissue attached
        • may contain DNA
  • Hair
    • other
      • root is embedded in follicle which is in equalized with the blood supply
        • anything taken into the body is distributed into growing hair (drugs, poisons)
          • esp. metals like Hg, As, Pb
        • time frame can be established as hair grows at a fixed rate