2 Introduction o Fibers are used in forensic science to create a link between crime and suspect o Through normal activities – We shed fibers – We picked up fibers o Very small fibers are classified as trace evidence o Collecting fibers within 24 hours is critical
Forensic Science: Fundamentals & Investigations, Chapter 4 3 How Forensic Scientists Use Fibers Fiber evaluation can show Type of fiber Color Possibility of violence Location of suspects Point of origin
Fiber Evidence o Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. o They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. o For analysis, they are first determined to be natural, manufactured, or a mix of both.
Forensic Science: Fundamentals & Investigations, Chapter 4 5 Sampling and Testing o Shedding—common form of fiber transfer o Microscopes reveal characteristic shapes and markings o Infrared spectroscopy reveals chemical structures to differentiate similar fibers o Destructive Testing Methods Burning fibers Dissolving fibers in various liquids
6 Testing for Identification Microscopic observation Burning—observation of how a fiber burns, the odor, color of flame, smoke and the appearance of the residue Thermal decomposition—gently heating to break down the fiber to the basic monomers Chemical tests—solubility and decomposition
Forensic Fiber Analysis o The world produced approximately 80 billion pounds of fabric in 1995, about half of which was cotton o 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 ). 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 o It could be argued that the large volume of fibers produced reduces the significance of a fiber association discovered in a criminal case. o Considering the volume of textiles produced worldwide each year, the number of textiles produced with any one fiber type and color is extremely small. o The likelihood of two or more manufacturers exactly duplicating all of the aspects of the textile is extremely remote
Forensic Science: Fundamentals & Investigations, Chapter 4 9 Sampling and Testing Compare fibers found on different suspects with those found at the crime scene
10 Fabric Fabric is made of fibers. Fibers are made of twisted filaments Types of fibers and fabric Natural—animal, vegetable or inorganic Artificial—synthesized or created from altered natural sources
Forensic Science: Fundamentals & Investigations, Chapter 4 11 Fiber Classification —Natural Fibers Animal fibers (made of proteins) : o Wool and cashmere from sheep o Mohair from goats o Angora from rabbits o Hair from alpacas, llamas, and camels o Silk from caterpillar cocoons (longer fiber does not shed easily) woven wool textile
Forensic Science: Fundamentals & Investigations, Chapter 4 12 Fiber Classification —Natural Fibers Plant fibers (made of the polymer cellulose) : o Absorb water o Insoluble in water o Very resistant to damage from harsh chemicals o Dissolvable only by strong acids o Becomes brittle over time
Forensic Science: Fundamentals & Investigations, Chapter 4 13 Fiber Classification —Natural Fibers Plant fibers: o Cotton—most common textile plant fiber (picture) o Coir from coconuts is durable o Hemp, jute, and flax from stems grow in bundles o Manila and sisal from leaves deteriorate more quickly
Forensic Science: Fundamentals & Investigations, Chapter 4 14 Fiber Classification —Natural Fibers Mineral Fibers: o Fiberglass—a fibrous form of glass o Asbestos—a crystalline structure
Forensic Science: Fundamentals & Investigations, Chapter 4 15 Fiber Classification —Synthetic Fibers o 50% of fabrics are artificially produced o Examples: Rayon Acetate Nylon Acrylic Polyester
Forensic Science: Fundamentals & Investigations, Chapter 4 16 Fiber Classification —Synthetic Cellulose Fibers Regenerated Fibers (derived from cellulose) : o Rayon – Most common in this group – Imitates natural fibers, but stronger o Celenese ® – Cellulose chemically combined with acetate – Found in many carpets o Polyamide nylon – Cellulose combined with three acetate units – Breathable and lightweight – Used in performance clothing
Forensic Science: Fundamentals & Investigations, Chapter 4 17 Fiber Classification —Synthetic Polymer Fibers o Polyester “Polar fleece” Wrinkle-resistant Not easily broken down by light or concentrated acid Added to natural fibers for strength o Nylon Easily broken down by light and concentrated acid Otherwise similar to polyester spandex nylon
Forensic Science: Fundamentals & Investigations, Chapter 4 18 Fiber Classification —Synthetic Polymer Fibers o Acrylic Inexpensive Tends to “ball” easily Substitute for artificial wool or fur o Olefins High performance Quick drying Resistant to wear
Forensic Science: Fundamentals & Investigations, Chapter 4 19 Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification
Forensic Science: Fundamentals & Investigations, Chapter 4 20 Yarns, fabrics, and textiles o Yarns—fibers (of any length, thick or thin, loose or tight) twisted or spun together o Blending fibers meets different needs (e.g., resistance to wrinkling) o Fibers are woven into fabrics or textiles Threads are arranged side by side (the warp) More threads are woven back and forth crosswise through the warp
Fiber Forensics o Generally, the analyst gets only a limited number of fibers to work with—sometimes only one. o Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home o Fibers are laid side by side for visual inspection through a microscope.
23 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.