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

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Miss Stanley Middle School Science Club Forensic Division

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Presentation transcript:

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 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?

Cotton Fiber

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

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

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

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?

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

Forensics at Work Jeffrey MacDonald The Telltale Rabbit