Presentation on theme: "Fiber Evidence Fiber evidence in court cases can be used to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers."— Presentation transcript:
Fiber Evidence Fiber evidence in court cases can be used to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers weighed heavily on the outcome of the case. Williams was convicted in 1982 based on carpet fibers that were found in his home, car and on several murder victims.
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.
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.
Fiber Collection 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.
Fibers Are considered class evidence Can be used as confirmation Are common trace evidence at a crime scene Can be characterized based on comparison of both physical and chemical properties
Fabric Fabric is made of fibers. Fibers are made of twisted filaments Types of fibers and fabric Natural—animal, vegetable or inorganic Synthetic/Artificial—synthesized or created from altered natural sources
Classification Natural fibers are classified according to their origin: Vegetable or cellulose Animal or protein Mineral
Cellulose Fibers Cotton—vegetable fiber; strong, tough, flexible, moisture absorbent, not shape retentive Rayon—chemically-altered cellulose; soft, lustrous, versatile Acetate/Cellulose acetate—cellulose chemically-altered to create an entirely new compound not found in nature.
Animal/Protein Fibers Wool—animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama, vicuna Silk—insect fiber that is spun by a silk worm to make its cocoon; fiber reflects light and has insulating properties
Mineral Fibers Asbestos—a natural fiber that has been used in fire-resistant substances Fiberglass—a manufactured inorganic fiber
Synthetic Fibers ( Made from derivatives of petroleum, coal and natural gas) Nylon—most durable of man-made fibers; extremely light weight Polyester—most widely used man- made fiber Acrylic—provides warmth from a lightweight, soft and resilient fiber 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.
Weave Terminology Yarn—a continuous strand of fibers or filaments, either twisted or not Blend—a fabric made up of two or more different types of fiber.
Woven The yarns pass under each other alternately Design resembles a checkerboard
Knitted Fabric Knitted fabrics are made by interlocking loops into a specific arrangement.
Filament Cross-Sections Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross-section. Use a microtome
Testing for Identification Microscopic observation Burning—observation of how a fiber burns, the odor, color of flame, smoke and the appearance of the residue
Testing for Identification - also Thermal decomposition Chemical tests Density Refractive Index Fluorescence Dyes – both components that make up dyes and The way a fabric accepts a particular dye can be separated and matched to an unknown.
Microscopy Fibers should be first examined with a stereomicroscope (40X). Physical features such as crimp, length, color, relative diameter, luster, apparent cross section, damage, and adhering debris should be noted. Fibers are then tentatively classified into broad groups such as synthetic or natural AND woven or knit.
Side-by-Side Comparisons. If all of the characteristics are the same under the stereoscope, the next step is to examine the fibers with a comparison microscope. This side-by-side and point-by-point examination is the best technique to discriminate between fibers, especially those that appear to be similar. The physical characteristics of them must be compared visually with the comparison microscope to determine if they are the same in the known and questioned samples. Photography is recommended for later demonstration.
Summary of Fiber Analysis In short, the fiber evidence is still about "class evidence.“ Even if fibers from two separate places can be matched via comparison, that does NOT mean they derive from the same source, and there is no fiber database that provides a probability of origin.
Fiber Samples to be Examined Natural Cotton woven Cotton knit Silk Linen Wool Synthetic Polyester woven Polyester knit Rayon Nylon Acrylic Satin