Trace Evidence Fibers Fibers n n Fibers are

Trace Evidence Fibers

Fibers n n Fibers are important pieces of evidence in incidences that involve personal contact. E. X. Homicide, Assault, or Sexual Offenses- in which cross-transfers may occur between the clothing of suspect and victim.

Fibers n Other offenses would include hit-andrun victims, fibers, threads or whole pieces of clothing could adhere to a part of a vehicle OR in a breaking-andentering attempt fibers or threads could remain to a screen or broken glass.

Fibers n n The value of fiber as a piece of trace evidenced depends on the ability to narrow the origin of that fiber to a limited number of sources or even to a single source. Unfortunately, the mass production of garments and fabrics has served to limit the value of fiber evidence in this respect.

Fibers n n n Two- broad groups of fabrics are natural and synthetic. Natural being, coming from plants or animals. Synthetic or man-made are madeup of Polymers.

Natural n n n Derived from plant or animals Animal fibers comprise a majority of natural fibers found at crime scenes Examples of Animal Fibers: n n Sheep (wool) Goats (mohair, cashmere) Camels, Llamas, Alpacas Fur Fibers - Mink, Rabbit, Beaver, Muskrat

Examples of Fibers Cotton Wool

Synthetic Fibers n Man-made materials began to make their wan in 1911 with Rayon, and then the development of Nylon in 1939.

Synthetic Fibers n n n Synthetic fibers are fibers that are produced solely from synthetic chemicals. Synthetic fibers came about when scientists developed a method of synthesizing long-chained molecules called polymers. Synthetic fibers include nylons, polyesters and acrylics.

Fibers n n A Polymer is a substance composed of a large number of atoms. These atoms are usually arranged in repeating units or monomers. An array of household, industrial and recreational products are manufactured from polymers; these include plastics, paints, adhesives and synthetic rubber.

Regenerated Fibers n n Regenerated fibers are fibers that come from processed cellulose that has been chemically treated and dissolved and forced through the small holes of a spinning jet or spinneret Common Regenerated fibers are rayon, acetate, and triacetate. Triacetate

Acetate vs. Triacetate

Fibers: Identification and Comparison n n Common Fit: One type of Fabric Comparison is the fitting together of Fabrics (like a puzzle). If the fabrics can be fitted together exactly at their torn edges, it is virtual certainty that the fabrics were of common origin.

Fibers n n Common fit occurs in a limited amount of cases. In most scenarios the examiner must use a side-by-side comparison of the standard/reference sample and crime-scene fibers. (Standard/Reference Sample- physical evidence whose origin is known, that can be compared to crime-scene evidence)

Fibers: Microscope n n Microscopic comparison- for color and diameter using a comparison microscope. If there is disagreement in these two characteristics, there is no reason to suspect a match.

Fibers: Dye composition n Another comparison of Fibers is their color. Though two fibers may seem to be the same color the dye compositions may be vastly different. The combination of dyes used to give a fiber its color or hue can be tested in several ways.

Fibers: Dye composition n n n Visible light microspectrophotometer. Thin Layer Chromatography (TLC) Chemical Composition Test Refractive Index Becke Line comparison Birefringence of Light Infrared Spectrophotometry

Fibers n Though fabrics may have some properties the same, each may differ in physical shape, appearance, and dyeability (all because of basic chemical structure)

Fibers n n Once it has been determined two fabrics are a match, the significance of the match is bound to be raised. There are no analytical techniques that will permit the association a fiber strand definitively to any single garment. Also, there are no statistical databases available to determine the probability of a fiber’s origin.

Fibers n Fiber association should not be discounted as evidence. There are thousands of differentcolored fibers in the environment. Also combine the fact that scientists compare the color of fibers, their size, shape, microscopic appearance, chemical composition, and dye content and it is unlikely to find two indistinguishable colored fibers from randomly selected sources.

Fibers n n n Collection and Preservation of Fiber Evidence. Fiber evidence can be associated with virtually every crime possible. For that reason the, fibers can be easily overlooked if they are not specifically being looked for. The task for the forensic scientist is to identify and preserve potential “carriers” of fiber evidence. “Carriers” could be clothing, carpet, knifes, sheets, car seats.

Fibers n In the lab the search for fiber evidence on clothing and other relevant objects is a time-consuming and tedious process. The search will test the skill and patience of the examiner.