2 IntroductionFibers are used in forensic science to create a link between crime and suspectThrough normal activitiesWe shed fibersWe picked up fibersVery small fibers are classified as trace evidenceCollecting fibers within 24 hours is criticalForensic Science: Fundamentals & Investigations, Chapter 4
3 How Forensic Scientists Use Fibers Fiber evaluation can showType of fiberColorPossibility of violenceLocation of suspectsPoint of originForensic Science: Fundamentals & Investigations, Chapter 4
4 Fiber EvidenceFibers 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.
5 Sampling and Testing Shedding—common form of fiber transfer Microscopes reveal characteristic shapes and markingsInfrared spectroscopy reveals chemical structures to differentiate similar fibersDestructive Testing MethodsBurning fibersDissolving fibers in various liquidsForensic Science: Fundamentals & Investigations, Chapter 4
6 Testing for Identification Microscopic observationBurning—observation of how a fiber burns, the odor, color of flame, smoke and the appearance of the residueThermal decomposition—gently heating to break down the fiber to the basic monomersChemical tests—solubility and decomposition
7 Forensic Fiber Analysis Why would this information be valuable to a forensic scientist?Forensic Fiber AnalysisThe world produced approximately 80 billion pounds of fabric in 1995, about half of which was cottonThe other approximately 44 billion pounds of fiber were manufactured or synthetic.Table 1. U.S. Annual Production for Manufactured Fibers: 1995 (millions of pounds)FiberProductPolyester3,887Nylon270Olefin521Rayon/Acetate/Triacetate498Acrylic/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.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.
8 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
9 Sampling and TestingCompare fibers found on different suspects with those found at the crime sceneForensic Science: Fundamentals & Investigations, Chapter 4
10 Fabric Natural—animal, vegetable or inorganic Fabric is made of fibers. Fibers are made of twisted filamentsTypes of fibers and fabricNatural—animal, vegetable or inorganicArtificial—synthesized or created from altered natural sources
11 Fiber Classification —Natural Fibers Animal fibers (made of proteins):Wool and cashmere from sheepMohair from goatsAngora from rabbitsHair from alpacas, llamas, and camelsSilk from caterpillar cocoons (longer fiber does not shed easily)woven wool textileForensic Science: Fundamentals & Investigations, Chapter 4
12 Fiber Classification —Natural Fibers Plant fibers (made of the polymer cellulose):Absorb waterInsoluble in waterVery resistant to damage from harsh chemicalsDissolvable only by strong acidsBecomes brittle over timeForensic Science: Fundamentals & Investigations, Chapter 4
13 Fiber Classification —Natural Fibers Plant fibers:Cotton—most common textile plant fiber (picture)Coir from coconuts is durableHemp, jute, and flax from stems grow in bundlesManila and sisal from leaves deteriorate more quicklyForensic Science: Fundamentals & Investigations, Chapter 4
14 Fiber Classification —Natural Fibers Mineral Fibers:Fiberglass—a fibrous form of glassAsbestos—a crystalline structureForensic Science: Fundamentals & Investigations, Chapter 4
15 Fiber Classification —Synthetic Fibers 50% of fabrics are artificially producedExamples:RayonAcetateNylonAcrylicPolyesterForensic Science: Fundamentals & Investigations, Chapter 4
16 Fiber Classification —Synthetic Cellulose Fibers Regenerated Fibers (derived from cellulose):RayonMost common in this groupImitates natural fibers, but strongerCelenese®Cellulose chemically combined with acetateFound in many carpetsPolyamide nylonCellulose combined with three acetate unitsBreathable and lightweightUsed in performance clothingForensic Science: Fundamentals & Investigations, Chapter 4
17 Fiber Classification —Synthetic Polymer Fibers Polyester“Polar fleece”Wrinkle-resistantNot easily broken down by light or concentrated acidAdded to natural fibers for strengthNylonEasily broken down by light and concentrated acidOtherwise similar to polyesterspandex nylonForensic Science: Fundamentals & Investigations, Chapter 4
18 Fiber Classification —Synthetic Polymer Fibers AcrylicInexpensiveTends to “ball” easilySubstitute for artificial wool or furOlefinsHigh performanceQuick dryingResistant to wearForensic Science: Fundamentals & Investigations, Chapter 4
19 Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibersunder MagnificationForensic Science: Fundamentals & Investigations, Chapter 4
20 Yarns, fabrics, and textiles Yarns—fibers (of any length, thick or thin, loose or tight) twisted or spun togetherBlending fibers meets different needs (e.g., resistance to wrinkling)Fibers are woven into fabricsor textilesThreads are arranged side by side (the warp) More threads are woven back andforth crosswise through the warpForensic Science: Fundamentals & Investigations, Chapter 4
22 Fiber ForensicsGenerally, 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 homeFibers are laid side by side for visual inspection through a microscope.
23 Fiber EvidenceFiber 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.