FORENSIC SCIENCE Trace Evidence Fiber 11/9/2018 FORENSIC SCIENCE Trace Evidence Fiber

Introduction Trace Evidence: any small pieces of material, man-made or naturally occurring Most common examples: Hair Fiber

Test Questions for Trace Evidence What is it? Is it man-made or natural? What is its source? How common is it? Can it be identified to a single source?

Fiber Evidence NOTE Fabric is the type of material and fibers are the “threads” that make up the fabric The use of fiber evidence in court cases is used many times to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers were the entire case. Williams was convicted in 1982 based on carpet fibers that were found in his home, car and on several murder victims (product rule).

Classification Fibers are classified according to their origin: Natural Vegetable Animal or protein Mineral Man-Made Regenerated Pure Synthetic

Vegetable or Plant Fibers Cotton Hemp Linen (Flax) Ramie Sisal

Protein Fibers Wool--animal fiber coming most often from sheep but may be goat (mohair,cashmere), rabbit (angora), camel, mink, beaver Silk--animal fiber that is spun by a silk worm to make its cocoon; fiber reflects light and has insulting properties Wool Fibers (400X)

Mineral Fibers Asbestos--a natural fiber that was used in fire-resistant substances Metallics (mylar)--a manufactured mineral fiber Fiberglass--another manufactured mineral fiber

Cellulose Fibers Rayon--first man-made fiber; soft, lustrous, versatile fiber Cellulose esters--cellulose is chemically altered to create an entirely new compound not found in nature. Acetate--less expensive, less polluting than rayon

Polymers Synthetic fibers are made of polymers which are long string of repeating chemical units. The word polymer means many (poly) units (mer). The repeating units of a polymer are called monomers. By varying the chemical structure of the monomers or by varying the way they are weaved together, polymers are created that have different properties. As a result of these differences, forensically they can be distinguished from one another.

Petroleum Plastics (Made from derivatives of petroleum, coal and natural gas) Nylon--most durable man-made fabric; extremely light weight Polyester--most widely used man-made fiber Acrylic--provides warmth from a lightweight, soft and resilient fabric Spandex--extreme elastic properties

Fabric Production Fabrics are composed of individual threads or yarns, made of fibers, that are knitted, woven, bonded, crocheted, felted, knotted or laminated. Most are either woven or knitted. The degree of stretch, absorbency, water repellence, softness and durability are all individual qualities of the different fabrics.

Woven Fabric Woven fabric are made by interlacing warp (lengthwise) and weft (filling) yarns. Warp run the length of the fabric and parallel to the selvage (the edge of the fabric). Weft cross over and under the warp threads. Types include: Plain Twill Satin

Woven Fabric PLAIN Simplest and most common weave Warp and weft pass under each other alternately Create even patterns of 1/1 and 2/2 Design resembles a checkerboard

Woven Fabric TWILL Create by passing the warp yarn over one to three weft yarns before going under one Makes a diagonal weave Design resembles a stair steps Denim is the most obvious example

Woven Fabric SATIN The yarn interlacing is not uniform Creates long floats Interlacing weave passes over four or more yarns Satin is the most obvious example

Knitted Fabric Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination. Either way, the yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric.. Diagram:

Identification and Comparison of Fibers Microscopic examination Color--compositional differences in the dyes Diameter Fibers surface--delustering particles that may be added by manufacturers Microspectrophotometer--compares fiber colors through spectral patterns Chromatography--gives a more detailed analysis of the dye composition

Identification and Comparison of Fibers (cont.) Polarizing microscope Can be used to determine the refractive indices of various fibers. The fiber is immersed in a fluid that has a comparable refractive index. The disappearance of the Becke line is observed under the microscope. In addition, fibers will absorb infrared light in a characteristic pattern. This can be observed through the use of an infrared microspectrophotometer and a microscope.

Collection of Fiber Evidence Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged. Make tape lifts of exposed skin areas of bodies and any inanimate objects Removed fibers should be folded into a small sheet of paper and stored in a paper bag

Uniqueness Establishing Individual Characteristics If there is only one source for the transfer material with a controlled environment where the contact took place If there is a method available to characterize the material, such as DNA Otherwise, trace evidence would have only class characteristics.

Figure F-1. Cross sections of several natural and synthetic fibers. Reproduced from Melone, et. al., Lab Manual for Crimminalistics, 6th ed, Prentice Hall.

Man, I was nailed when those forensic guys found fibers from the kid’s math assignment in my teeth.