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Fiber and Threads

Fiber and Threads. How are fibers found at a scene helpful? Why would fibers be less than helpful when found at a scene?. Types of Fibers. Natural fibers – derived from plants or animals Manufactured fibers – fibers derived from either natural or synthetic polymers. Natural Fibers.

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Fiber and Threads

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  1. Fiber and Threads • How are fibers found at a scene helpful? • Why would fibers be less than helpful when found at a scene?

  2. Types of Fibers • Natural fibers – derived from plants or animals • Manufactured fibers – fibers derived from either natural or synthetic polymers

  3. Natural Fibers • Which type of natural fibers do you think are most often encountered at crime scenes? • Hair • Fur • Use microscopic analysis to identify • What is the most prevalent PLANT fiber?

  4. Cotton Fiber

  5. Identification and Comparison of Manufactured Fibers • 1st Step: Microscopic Examination of fibers • To compare color and diameter • Uses a comparison microscope • If negative, no point going further.

  6. Microscopic Examination • Other features to compare: • Lined markings on the surface • Pitting of the surface • Cross-sectional (???) shape • Comparison of dye composition of same-colored fibers • Microspectrophotometer • Chromatographic separation of the dye constituents

  7. Images – pp.373-374

  8. Identification and Comparison of Manufactured Fibers • 2nd Step: Chemical Composition to determine and compare what class of fibers each sample belongs to. • 3rd Step: Other, more complicated tests

  9. Significance of Fiber Evidence • Does a fiber match mean the fiber came from the garment in question? • What are the chances that a match - including size shape, microscopic appearance, chemical composition, and dye content - would be wrong?

  10. Collection of Evidence • How? • Bag whole articles separately – clothing, bedding, carpets, car seats, etc. • Remove stray fibers • Either way, VERY tedious and time-consuming

  11. Forensics at Work • Jeffrey MacDonald • The Telltale Rabbit

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