Forensics of Fiber Analysis

Fibers A fiber is the smallest unit of a textile material that has a length many times greater than its diameter. Fibers can occur naturally as plant and animal fibers, but they can also be man-made. A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric. The type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers and the significance of fiber associations.

Natural Fibers Many different natural fibers originating from plants and animals are used in the production of fabric. Cotton fibers are the plant fibers most commonly used in textile materials the type of cotton, fiber length, and degree of twist contributing to the diversity of these fibers. Cotton fibers

Natural Fibers vs Manufactured Natural fibers come from plants (cotton) or animals (wool). Manufactured fibers are synthetics like rayon, acetate, and polyester, which are made from long chains of molecules called polymers.

Other plant fibers Flax (linen), ramie, sisal, jute, hemp, kapok, and coir. The identification of less common plant fibers at a crime scene or on the clothing of a suspect or victim would have increased significance. Flax fibers viewed with polarized light

Animal Fiber: Wool Wool is the most frequently used in the production of textile materials and the most common wool fibers originate from sheep. Finer woolen fibers are used in the production of clothing coarser fibers are found in carpet. Fiber diameter and degree of scale protrusion of the fibers are other important characteristics. Wool fibers

Other Animal Fibers Although sheep's wool is most common, woolen fibers from other animals may also be found. These include and others. The identification of less common animal fibers at a crime scene or on the clothing of a suspect or victim would have increased significance.

Fiber Number The number of fibers on the clothing of a victim identified as matching the clothing of a suspect is important in determining actual contact. The greater the number of fibers, the more likely that contact actually occurred between these individuals

Fiber Evidence Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. For analysis, they are first determined to be natural, manufactured, or a mix of both.

Fiber Evidence The problem with fiber evidence is that fibers are not unique. Unlike fingerprints or DNA, they cannot pinpoint an offender in any definitive manner. There must be other factors involved, such as evidence that the fibers can corroborate or something unique to the fibers that set them apart.

Forensics of Fiber Analysis Cross transfers of fiber often occur in cases in which there is person-to-person contact Investigators hope that fiber traceable back to the offender can be found at the crime scene, as well as vice versa. Success in solving crimes often hinge on the ability to narrow the sources for the type of fiber found, as the prosecution did with their probability theory on the fibers

Forensic Fiber Analysis The world produced approximately 80 billion pounds of fabric in 1995, about half of which was cotton The other approximately 44 billion pounds of fiber were manufactured or synthetic. Table 1. U.S. Annual Production for Manufactured Fibers: 1995 (millions of pounds) FiberProduct Polyester3,887 Nylon270 Olefin521 Rayon/Acetate/Triace tate 498 Acrylic/Modacrylic432 (Table 1 [6]). All these fibers were used in a variety of applications including but not limited to clothing, household textiles, carpeting, and industrial textiles. Why would this information be valuable to a forensic scientist?

Forensic Fiber Analysis It could be argued that the large volume of fibers produced reduces the significance of a fiber association discovered in a criminal case. Considering the volume of textiles produced worldwide each year, the number of textiles produced with any one fiber type and color is extremely small. The likelihood of two or more manufacturers exactly duplicating all of the aspects of the textile is extremely remote