Fibers & textile Analysis CHAPTER 4 Fibers & textile Analysis Forensic Science: Fundamentals & Investigations, Chapter 4

Introduction Fibers are used in forensic science to create a link between crime and suspect Through normal activities We shed fibers We picked up fibers Very small fibers are classified as trace evidence Collecting fibers within 24 hours is critical Forensic Science: Fundamentals & Investigations, Chapter 4

How Forensic Scientists Use Fibers Fiber evaluation can show Type of fiber Color Possibility of violence Location of suspects Point of origin Forensic Science: Fundamentals & Investigations, Chapter 4

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.

Sampling and Testing Shedding—common form of fiber transfer Microscopes reveal characteristic shapes and markings Infrared spectroscopy reveals chemical structures to differentiate similar fibers Destructive Testing Methods Burning fibers Dissolving fibers in various liquids Forensic Science: Fundamentals & Investigations, Chapter 4

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 Why would this information be valuable to a forensic scientist? 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) Fiber Product Polyester 3,887 Nylon 270 Olefin 521 Rayon/Acetate/Triacetate 498 Acrylic/Modacrylic 432 (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. It could be argued that the large volume of fibers produced reduces the significance of a fiber association discovered in a criminal case. It can never be stated with certainty that a fiber originated from a particular textile because other textiles are produced using the same fiber types and color. The inability to positively associate a fiber to a particular textile to the exclusion of all others, however, does not mean that a fiber association is without value. 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 (see endnote 2). Beyond the comments made previously about color, shade tolerance differs between dyeing companies. Therefore, color may vary demonstrably from batch to batch. Also, the life span of a particular fabric must be considered. Only so much of a given fabric of a particular color and fiber type is produced, and it will eventually end up being destroyed or dumped in a landfill.

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

Sampling and Testing Compare fibers found on different suspects with those found at the crime scene Forensic Science: Fundamentals & Investigations, Chapter 4

Fabric Natural—animal, vegetable or inorganic 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

Fiber Classification —Natural Fibers Animal fibers (made of proteins): Wool and cashmere from sheep Mohair from goats Angora from rabbits Hair from alpacas, llamas, and camels Silk from caterpillar cocoons (longer fiber does not shed easily) woven wool textile Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Plant fibers (made of the polymer cellulose): Absorb water Insoluble in water Very resistant to damage from harsh chemicals Dissolvable only by strong acids Becomes brittle over time Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Plant fibers: Cotton—most common textile plant fiber (picture) Coir from coconuts is durable Hemp, jute, and flax from stems grow in bundles Manila and sisal from leaves deteriorate more quickly Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Mineral Fibers: Fiberglass—a fibrous form of glass Asbestos—a crystalline structure Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Fibers 50% of fabrics are artificially produced Examples: Rayon Acetate Nylon Acrylic Polyester Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Cellulose Fibers Regenerated Fibers (derived from cellulose): Rayon Most common in this group Imitates natural fibers, but stronger Celenese® Cellulose chemically combined with acetate Found in many carpets Polyamide nylon Cellulose combined with three acetate units Breathable and lightweight Used in performance clothing Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Polymer Fibers Polyester “Polar fleece” Wrinkle-resistant Not easily broken down by light or concentrated acid Added to natural fibers for strength Nylon Easily broken down by light and concentrated acid Otherwise similar to polyester spandex nylon Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Polymer Fibers Acrylic Inexpensive Tends to “ball” easily Substitute for artificial wool or fur Olefins High performance Quick drying Resistant to wear Forensic Science: Fundamentals & Investigations, Chapter 4

Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification Forensic Science: Fundamentals & Investigations, Chapter 4

Yarns, fabrics, and textiles Yarns—fibers (of any length, thick or thin, loose or tight) twisted or spun together Blending fibers meets different needs (e.g., resistance to wrinkling) 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 Forensic Science: Fundamentals & Investigations, Chapter 4

Weave Patterns Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Forensics Generally, the analyst gets only a limited number of fibers to work with—sometimes only one. Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home Fibers are laid side by side for visual inspection through a microscope.

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.