Forensic Examination of Fibers

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Presentation transcript:

Forensic Examination of Fibers

Fiber Evidence Collection Critical in the first 24 hours. After that it is estimated that 95% of all fibers are lost.

Types of Fibers - Natural Natural fibers – fibers derived entirely from animal or plant sources. Includes 1. Animal hairs – wool, mohair, cashmere, furs, and silk 2. Plant fibers – cotton, coir, hemp, jute, sisal, and flax 3. Mineral fibers – asbestos, fiberglass

Types of Fibers - Synthetic AKA Manufactured fibers – fibers derived from either natural or synthetic polymers. Includes materials such as acetate, acrylic, melamine, nylon, polyester, rayon, and spandex.

Polymers Polymer - a substance composed of a large number of atoms that are usually arranged in repeating units.

Polymers are made of single units called monomers bonded together. Monomers are molecules - two or more atoms held together by chemical bonds. When a molecule has a high molecular mass it is known as a macromolecule.

Fiber Identification Microscopic Examination - Color and diameter match are critical.

Microspectrophotometer Microspectrophotometer - an instrument that links microscope to a spectrophotometer. This device allows an analyst to view a particle under a microscope while a beam of light is directed at the particle to obtain its absorption spectrum. For fibers this allows for a comparison of colors of fibers through their spectral patterns.

Analytic Techniques Used in Fiber Examination Chemical Composition – there are numerous chemical tests that can be performed but they are all destructive.

Birefringence (refractive differences) – polarized white light is used and is nondestructive. A property found in manufactured or synthetic fibers.

Infrared Absorption – fibers absorb light and vibrate at specific frequencies. (nondestructive)

Collection and Preservation of Fiber Evidence Relevant articles of clothing should be packaged carefully in paper bags. Care must be taken to keep articles from touching other articles. Loose fibers should be collected and packaged in paper bindles.