1 SUPA Forensics Fiber Analysis
2 Chapter 6: Fibers “Wherever he steps, whatever he touches, whatever he leaves even unconsciously, will serve as silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool marks he leaves, the paint he scratches, the blood or semen he deposits or collects—all of these and more bear mute witness against him. This is evidence that does not forget.” —Paul L. Kirk (1902 – 1970) Forensic scientist
3 Kendall/Hunt Publishing CompanyFibers Students will learn: The student will learn: How fibers can be used as circumstantial evidence to link the victim, suspect, and crime scene. Why fibers are class evidence. Why statistics are important in determining the value of evidence. Kendall/Hunt Publishing Company
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
5 Why Questioning fibersWhy Questioning fibers? How close can you place the suspect/victim to the CS? Type of fiber?, composition, scarcity, Color? dye/pigment type Number found: what is the correlation? The more fibers the more violent/ longer the contact Where was if found? Textile origin? Carpet, upholstery Multiple fiber transfer? Inc # of sources Type of crime committed? Violent, B+E, kidnapping Time between crime and discovery of fibers?
6 How Forensic Scientists Use FibersFiber evaluation can show Type of fiber Color Possibility of violence Location of suspects Point of origin Forensic Science: Fundamentals & Investigations, Chapter 4
7 Kendall/Hunt Publishing CompanyFibers Students will be able to: Distinguish and identify different types of fibers. Understand polymerization. Carry out an experiment in thin-layer chromatography. Judge the probative value of fiber evidence. Design and carry out scientific investigations. Use technology and mathematics to improve investigations and communications. Kendall/Hunt Publishing Company
8 Kendall/Hunt Publishing CompanyFibers Are considered class evidence Have probative value Are common trace evidence at a crime scene Can be characterized based on comparison of both physical and chemical properties Kendall/Hunt Publishing Company
9 Sampling and Testing Shedding—common form of fiber transferMicroscopes 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
10 Sampling and Testing Compare fibers found on different suspects with those found at the crime scene Forensic Science: Fundamentals & Investigations, Chapter 4
11 Fiber and textile Most common fiber transfer is? Shedding of textiles.Fibers are classified as: Natural fiber: Animal, plant, mineral Synthetic Man made polymers . 12/5/2017
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13 Natural fibers: fibers derived entirely from animal or plant sourcesMan-made fibers: fibers derived from either natural or synthetic polymers; the fibers are typically made by forcing the polymeric material through the holes of a spinneret Polymer: a substance composed of a large number of atoms. These atoms are usually arranged in repeating units or monomers
14 Molecules: two or more atoms held together by chemical bondsMacromolecule: a molecule with a high molecular mass Monomer: the basic unit of structure from which a polymer is constructed
15 Kendall/Hunt Publishing CompanyFabric 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 Kendall/Hunt Publishing Company
16 Kendall/Hunt Publishing CompanyTypes of Fibers Synthetic Rayon Nylon Acetate Acrylic Spandex Polyester Natural Silk Cotton Wool Mohair Cashmere Kendall/Hunt Publishing Company
17 Natural Fibers
18 Natural Fibers Are ... Nonthermoplasticdo not soften when heat is applied Particularly susceptible to microbial decomposition (mildew & rot) cellulose based decomposed by aerobic bacteria & fungi protein based decomposed by bacteria and molds moths, carpet beetles, termites, silverfish
19 Natural Fibers Classified according to their originvegetable or cellulose based animal or protein based mineral class asbestos
20 Fiber Classification —Natural FibersAnimal 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
21 WOOL Microscopic images of wool fibers
22 Wool
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24 Fiber Classification —Natural FibersPlant 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
25 Fiber Classification —Natural FibersPlant 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
26 Cotton
27 Cotton Cotton fiber, once it has been processed to remove seeds and traces of wax, protein, etc., consists of nearly pure cellulose, a natural polymer. Cotton production is very efficient, in the sense that ten percent or less of the weight is lost in subsequent processing to convert the raw cotton bolls (seed cases) into pure fiber. The cellulose is arranged in a way that gives cotton fibers a high degree of strength, durability, and absorbency.
28 Cotton Micrograph
29 Kendall/Hunt Publishing CompanyClassification Natural fibers are classified according to their origin: Vegetable or cellulose Animal or protein Mineral Kendall/Hunt Publishing Company
30 Kendall/Hunt Publishing CompanyCellulose Fibers Cotton—vegetable fiber; strong, tough, flexible, moisture absorbent, not shape retentive Rayon—chemically-altered cellulose; soft, lustrous, versatile Cellulose acetate—cellulose chemically-altered to create an entirely new compound not found in nature. Kendall/Hunt Publishing Company
31 Fiber Comparison Can you tell the difference(s) between the cotton onthe left and the rayon on the right? Kendall/Hunt Publishing Company
32 Kendall/Hunt Publishing CompanyProtein 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 Kendall/Hunt Publishing Company
33 Spider Silk Spinnerets
34 Spider Silk SpinneretsScientists don't know exactly how spiders form silk, but they do have a basic idea of the spinning process. Spiders have special glands that secrete silk proteins (made up of chains of amino acids), which are dissolved in a water-based solution. The spider pushes the liquid solution through long ducts, leading to microscopic spigots on the spider's spinnerets. Spiders typically have two or three spinneret pairs, located at the rear of the abdomen.
35 Kendall/Hunt Publishing CompanyProtein 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 Kendall/Hunt Publishing Company
36 Artificial Fibers and Polymeric Fibers
37 Polymers Long strings of repeating chemical units poly (many)mer (unit)
38 Fibers are Polymers
39 Cellulose Based FibersCotton Jute sacks & bags burlap backing for tufted carpets & hooked rugs Oriental rugs twines & ruff cordage
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41 Protein Based Fibers More vulnerable to environmental degradation than cellulose based fibers Wool (sheep) Mohair (goat) fiber structure similar to wool half the scales of wool scales lie flat (smooth surface) <1% of fibers have a medulla Silk
42 Helical Proteins Based on alpha-keratin
43 A Hair Fiber
44 Sheet Proteins Based on beta-keratin
45 Mineral Polymers Asbestosany of several minerals that readily separate into long, flexible fibers Chrysotile (hydrous magnesium silicate) Mg3Si2O5(OH)4 formerly used in shingles insulation cement pipes
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47 Fiber Classification —Natural FibersMineral Fibers: Fiberglass—a fibrous form of glass Asbestos—a crystalline structure Forensic Science: Fundamentals & Investigations, Chapter 4
48 Kendall/Hunt Publishing CompanyMineral Fibers Asbestos—a natural fiber that has been used in fire-resistant substances Rock wool—a manufactured mineral fiber Fiberglass—a manufactured inorganic fiber Kendall/Hunt Publishing Company
49 Man/Woman-Made Fibers
50 Man-Made Fibers Regenerated Fibers Synthetic Fibersderived from naturally occurring polymers rayon acetate Synthetic Fibers made of polymers that do not occur naturally polyesters polyamides
51 Polymers are fibers too!Polymers arranged in fibers like this can be spun into threads and used as textiles. The clothes you're wearing are made out of polymeric fibers. So is carpet. So is rope. Here are some of the polymers which can be drawn into fibers: Polyethylene Polypropylene Nylon Polyester Kevlar and Nomex Polyacrylonitrile Cellulose Polyurethanes
52 Kendall/Hunt Publishing CompanySynthetic 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 Kendall/Hunt Publishing Company
53 Kendall/Hunt Publishing CompanyPolymers Synthetic fibers are made of polymers which are long chains 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 joined together, polymers are created that have different properties. As a result of these differences, forensically they can be distinguished from one another. Kendall/Hunt Publishing Company
54 Filament Cross-SectionsSynthetic 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. Kendall/Hunt Publishing Company
55 Polyesters Polyethylene terephthalate (PET)X=O can be melt-spun into very practical and cheap fibers Dacron Clothing, furnishings, carpets, tire cord
56 PET
57 Polyamides Polyhexamethylene adipamide (Nylon 6,6)X= NH synthesized from adipic acid and hexamethylenediamine each contain six carbon atoms Nylon 6 or Nylon 6,6 Apparel, carpets, and tire cord
58 Nylon 6,6
59 Hx of Nylon Nylons are one of the most common polymers used as a fiber. Nylon is found in clothing all the time, but also in other places, in the form of a thermoplastic. Nylon's first real success came with it's use in women's stockings, in about They were a big hit, but they became hard to get, because the next year the United States entered World War II, and nylon was needed to make war materials, like parachutes and ropes. But before stockings or parachutes, the very first nylon product was a toothbrush with nylon bristles.
60 NYLON examples Fishing net rope backpack Dog harness
61 Nylon Polarizing microscope image of a nylon fiber.
62 TEM Nylon 6
63 SEM Nylon mcm
64 Nylon strength In that case I suppose I can tell you that fibers have their drawbacks. While they have good tensile strength, that is, they're strong when you pull or stretch them, they usually have bad compressional strength, that is, they're weak when you try to squash or compress them. Also, fibers tend to be strong only in one direction, the direction in which they're oriented. If you pull in them in the direction at right angles to their orientation, they tend to be weak
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66 Nylons are also called polyamides, because of the characteristic amide groups in the backbone chain.Proteins, such as the silk nylon was made to replace, are also polyamides. These amide groups are very polar, and can hydrogen bond with each other. Because of this, and because the nylon backbone is so regular and symmetrical, nylons are often crystalline, and make very good fibers
67 Nylon 6,6 The nylon in the pictures on this page is called nylon 6,6, because each repeat unit of the polymer chain has two stretches of carbon atoms, each being six carbon atoms long. Other nylons can have different numbers of carbon atoms in these stretches.
68 Making Nylon 6,6
69 Polyesters Polyesters have hydrocarbon backbones which contain ester linkages, hence the name.
70 Polyester as a fiber The ester groups in the polyester chain are polar, with the carbonyl oxygen atom having a somewhat negative charge and the carbonyl carbon atom having a somewhat positive charge. The positive and negative charges of different ester groups are attracted to each other. This allows the ester groups of nearby chains to line up with each other in crystal form, which is why they can form strong fibers
71 TEM Polyester Woven
72 Aromatic Polyesters (Aramids)Flexible CH2 groups replaced by rigid aromatic rings High melting Flame retardant clothing, bullet-poof vests, tire cord
73 Nomex and Kevlar Aramids are a family of nylons, including Nomex® and Kevlar®. Kevlar® is used to make things like bullet proof vests and puncture resistant bicycle tires. I suppose one could even make bullet proof bicycle tires from Kevlar® if one felt the need.
74 Nomex and Kevlar Blends of Nomex® and Kevlar® are used to make fireproof clothing. Nomex® is what keeps the monster truck and tractor drivers from burning to death should their fire-breathing rigs breathe a little too much fire. Thanks to Nomex®, an important part of American culture can be practiced safely. Firefighters turnout gear
75 Kevlar Kevlar® is a polyamide, in which all the amide groups are separated by para-phenylene groups, that is, the amide groups attach to the phenyl rings opposite to each other, at carbons 1 and 4.
76 Kevlar Kevlar is the DuPont Company's brand name for material made out of synthetic fiber of poly-paraphenylene terephthalamide which is constructed of para-aramid fibers that the company claims is five times stronger than the same weight of steel, while being lightweight, flexible and comfortable. It is also very heat resistant and decomposes above 400 °C without melting
77 Kevlar Hx and uses It was invented by Stephanie Kwolek of DuPont from research into high performance polymers, and patented by her in 1966 and first marketed in Kevlar is a registered trademark of E.I. du Pont de Nemours and Company. Originally intended to replace the steel belts in tires, it is probably the most well known name in soft armor such as bulletproof vests. It is also used in extreme sports equipment, high-tension drumhead applications, animal handling protection, composite aircraft construction, fire suits, yacht sails, as an asbestos replacement, sometimes in loudspeaker cones, and recently, even in R/C model helicopter blades.
78 Kevlar
79 Nomex
80 Nomex
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82 Cellulose Cellulose is one of many polymers found in nature. Wood, paper, and cotton all contain cellulose. Cellulose is an excellent fiber. Wood, cotton, and hemp rope are all made of fibrous cellulose. Cellulose is made of repeat units of the monomer glucose. This is the same glucose which your body metabolizes in order to live, but you can't digest it in the form of cellulose. Because cellulose is built out of a sugar monomer, it is called a polysaccharide.
83 Cellulose
84 Regenerated Fibers Fibers consisting of both natural and artificial components
85 Manufacture of Synthetic FibersMelted or dissolved polymer is forced through fine holes of a spinnerette Similar to a bathroom showerhead A fine filament is produced
86 Manufacture of Synthetic Fiberspolymer molecules are aligned parallel to the length of the filament crystallinity imparts stiffness & strength
87 Wood Cellulose Wet structure
88 Common synthetic fibers include: Synthetic fibers are the result of extensive research by scientists to increase and improve upon the supply of naturally occurring animal and plant fibers that have been used in making cloth and rope. In general, synthetic fibers, or man-made fibers, are created by forcing, usually through extrusion, fiber forming materials through holes (called spinnerets) into the air, forming a thread. Common synthetic fibers include: Rayon (1910) (an artificial fiber, but not truly synthetic) Acetate (1924) Nylon (1939) Modacrylic (1949) Olefin (1949) Acrylic (1950) Polyester (1953) PLA (2002) Specialty synthetic fibers include: Vinyon (1939) Saran (1941) Spandex (1959) Vinalon (1939) Aramids (1961) - known as Nomex, Kevlar and Twaron Modal (1960's) PBI (Polybenzimidazole fiber) (1983) Sulfar (1983) Lyocell (1992) Dyneema/Spectra (1979) M-5 (PIPD fibre) Orlon Zylon (PBO fibre) Vectran (TLCP fibre
89 Fibers comparison methods
90 Microscopic ComparisonColor Diameter Lengthwise striations on surface Pitting with delustering particles TiO2 reduces shine
91 Dye Composition Visible Light Microspectrophotometrynon-destructive fiber mounted on a microscope slide Chromatographic separation of dye components dye extracted from fiber with solvent TLC of questions extract vs. control extract
92 Manufacture of Synthetic Fibers
93 Fiber Composition Attempts to place fiber into both a broad generic class & a subclass Many man-made fibers exhibit birefringence light passing through fiber emerges as two rays one parallel to fiber length one perpendicular to fiber length Table 8-2
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96 Nylon 6 Nylon 6, 10
97 Testing for IdentificationMicroscopic 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 Kendall/Hunt Publishing Company
98 Testing for IdentificationDensity—mass of object divided by the volume of the object Refractive Index—measuring the bending of light as it passes from air into a solid or liquid Fluorescence—used for comparing fibers as well as spotting fibers for collection Kendall/Hunt Publishing Company
99 Kendall/Hunt Publishing CompanyDyes Components that make up dyes can be separated and matched to an unknown. There are more than 7000 different dye formulations. Chromatography is used to separate dyes for comparative analysis. The way a fabric accepts a particular dye may also be used to identify and compare samples. Kendall/Hunt Publishing Company
100 Identification and Comparison of FibersFourier Transform Infrared analysis (FTIR)—based on selective absorption of wavelengths of light Optical microscopy—uses polarizing light and comparison microscopes Pyrolysis gas chromatography-mass spectrometry (PGC-MS)—burns a sample under controlled conditions, separates and analyzes each combustion product Kendall/Hunt Publishing Company
101 Collection of Fiber Evidence
102 Collection of Fiber EvidenceBag 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. Kendall/Hunt Publishing Company
103 Collection of Fiber EvidenceInvestigator must identify & preserve potential fiber “carriers” Clothing items are packaged individually in paper bags different items must not be placed on the same surface before being bagged Tape lifts of exposed skin areas of bodies & inanimate objects
104 Collection of Fiber EvidenceIf fibers must be removed from an object clean forceps fold fiber into a small sheet of paper store in paper bag
105 Collection of 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.
106 Narrow it down Natural fibers come from plants (cotton) or animals (wool). Manufactured fibers are synthetics like rayon, acetate, and polyester, which are made from long chains of molecules called polymers. To determine the shape and color of fibers from any of these fabrics, a microscopic examination is made.
107 Non-invasive first 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, and the fibers are laid side by side for visual inspection through a microscope.
108 Microscopy A compound microscope uses light reflected from the surface of a fiber and magnified through a series of lenses, while the comparison microscope (two compound microscopes joined by an optical bridge) is used for more precise identification.
109 Spectrophotometry Another useful instrument is the spectrometer, which separates light into component wavelengths. In 1859, two German scientists discovered that the spectrum of every organic element has a uniqueness to its constituent parts. By passing light through something to produce a spectrum, the analyst can read the resulting lines, called "absorption lines." That is, the specific wavelengths that are selectively absorbed into the substance are characteristic of its component molecules. Then a spectrophotometer measures the light intensities, which yields a way to identify different types of substances.
110 Microscope + Spectrophotometer = MicrospectrophotometerA combination of these instruments for the most effective forensic analysis is the micro-spectrophotometer. The microscope locates minute traces or shows how light interacts with the material under analysis. Linking this to a computerized spectrophotometer increases the accuracy. The scientist can get both a magnified visual and an infrared pattern at the same time, which increases the number of identifying characteristics of any given material
111 Step 1 The first step in fiber analysis is to compare color and diameter. If there is agreement, then the analysis can go into another phase. Dyes can also be further analyzed with chromatography, which uses solvents to separate the dye's chemical constituents. Under a microscope, the analyst looks for lengthwise striations or pits on a fiber's surface, or unusual shapes---as with the one short and two long arms of the trilobal fibers in the Williams case.
112 Fiber Classification —Synthetic Fibers50% of fabrics are artificially produced Examples: Rayon Acetate Nylon Acrylic Polyester Forensic Science: Fundamentals & Investigations, Chapter 4
113 Fiber Classification —Synthetic Cellulose FibersRegenerated 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
114 Fiber Classification —Synthetic Polymer FibersPetroleum base Very different from other fibers Monomers join to form polymers Fibers are spun together into yarns No internal structures Uniform diameters Forensic Science: Fundamentals & Investigations, Chapter 4
115 Fiber Classification —Synthetic Polymer FibersPolyester “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
116 Fiber Classification —Synthetic Polymer FibersAcrylic 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
117 Comparison of Natural and Synthetic FibersVisual Diagnostics of Some Common Textile Fibers under Magnification Forensic Science: Fundamentals & Investigations, Chapter 4
118 Yarns, fabrics, and textilesYarns—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 (the weft) are woven back and forth crosswise through the warp Forensic Science: Fundamentals & Investigations, Chapter 4
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120 Weave Patterns Forensic Science: Fundamentals & Investigations, Chapter 4
121 Kendall/Hunt Publishing CompanyWeave Terminology Yarn—a continuous strand of fibers or filaments, either twisted or not Warp—lengthwise yarn Weft—crosswise yarn Blend—a fabric made up of two or more different types of fiber. Kendall/Hunt Publishing Company
122 Kendall/Hunt Publishing CompanyWeave Patterns Kendall/Hunt Publishing Company
123 Kendall/Hunt Publishing CompanyPlain Weave The simplest and most common weave pattern The warp and weft yarns pass under each other alternately Design resembles a checkerboard Kendall/Hunt Publishing Company
124 Kendall/Hunt Publishing CompanyTwill Weave The warp yarn is passed over one to three weft yarns before going under one Makes a diagonal weave pattern Design resembles stair steps Denim is one of the most common examples Kendall/Hunt Publishing Company
125 Kendall/Hunt Publishing CompanySatin Weave The yarn interlacing is not uniform Creates long floats Interlacing weave passes over four or more yarns Satin is the most obvious example Kendall/Hunt Publishing Company
126 Kendall/Hunt Publishing CompanyKnitted 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. Kendall/Hunt Publishing Company
127 Summary Fibers are a form of class evidence. Fibers are a form of trace evidence. Fibers are spun into yarns having specific characteristics. Yarns are woven, with different patterns, into clothing or textiles. Fiber evidence is gathered using different techniques. Forensic Science: Fundamentals & Investigations, Chapter 4
128 Summary Fibers are analyzed using burn tests, tests for solubility in different solutions, polarized light microscopy, or infrared spectroscopy. Fibers are classified as natural or synthetic. Natural fiber sources include: Animal hair Plant seeds, fruit, stems, or leaves Minerals. Forensic Science: Fundamentals & Investigations, Chapter 4
129 Kendall/Hunt Publishing CompanyFiber 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. Kendall/Hunt Publishing Company
130 Kendall/Hunt Publishing CompanyMore about Fibers For additional information about fibers and other trace evidence, check out Court TV’s Crime Library at: Kendall/Hunt Publishing Company
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132 CASE STUDY
133 Fibers and Probability Theory Wayne Williams CaseFrom 1979 to 1981, someone was killing Atlanta's youth. More than twenty-five black males, some as young as nine, had been strangled, bludgeoned or asphyxiated. A few females were killed and some children were just missing, but all potential leads turned into dead ends. The only real clue---which was valuable only if a suspect surfaced---was the presence on several of the bodies and their clothing of some kind of fiber threads. A few also bore strands of what was determined to be hair from a dog.
134 These specimens were all sent to the Georgia State Crime Laboratory for analysis, and technicians there isolated two distinct types: a violet-colored acetate fiber and a coarse yellow-green nylon fiber with the type of tri-lobed (three branch) qualities associated with carpets. They searched unsuccessfully for the manufacturer.
135 Wayne Williams Case Since the unknown predator seemed to favor the Chatahoochee River, the police set up a stakeout. On May 22, 1981, this strategy appeared to pay off. In the early morning hours, the stakeout patrol heard a loud splash. Someone had just thrown something rather large into the river. On the James Jackson Parkway Bridge, they saw a white Chevrolet station wagon, and when they stopped it, they learned that the driver's name was Wayne Williams. He was a 23 year-old black photographer and music promoter. They questioned him, but when he said he'd just dumped some garbage they let him go. (Later he would claim that he'd come there to see the stakeout, having heard about it from friends in the police force.)
136 Only two days later, the police found what they believed had been the source of the splash---the body of 27-year-old Nathaniel Cater. He was dredged up about a mile from the bridge, and despite his murderer's carefulness, a single yellow-green carpet fiber was found in his hair.
137 The police got a search warrant for Wayne Williams' home and car, and the search turned up a valuable piece of evidence: The floors of Williams' home were covered with yellow-green carpeting, and he also had a dog. Comparisons from the samples removed from the victims showed good consistency with Williams' carpet. Although Williams claimed to have an alibi, the description he gave of his movements the night they found him on the bridge was partly false and partly unsubstantiated. Three separate polygraph tests indicated deception on Williams' part.
138 Then FBI experts analyzed samples from his rugsThen FBI experts analyzed samples from his rugs. With special equipment, and in consultation with Du Pont, they managed to ascertain that the fibers came from a Boston-based textile company. The fiber was called Wellman 181B and it had been sold to numerous carpet companies. Each uses its own dye, so that made it possible to narrow down the likely source, which was the West Point Pepperell Corporation in Georgia. Their "Luxaire English Olive" color matched that found in Wayne William's home. There were also similarities between the hair from Williams' dog and the dog hair found on several victims.
139 Too good to be true However, many other homes had this carpeting installed, too. Thus, it had to be determined just how likely it was that Williams' carpeting was unique enough to persuade a jury of his connection to the murders. The next step was calculating the odds.
140 A look into company records turned up information that they had only made that type of carpet during a one-year span of time, with over 16,000 yards of carpet distributed throughout the South. In comparison with the total amount of carpet distributed across the country, this was a very small sample. That made the statistical probability of the carpet being in any one person's home to be slight, if it could be assumed that Luxaire English Olive had been fairly evenly distributed. Altogether they figured that around eighty-two homes in Georgia were carpeted with Luxaire English Olive. That meant the odds were stacked against finding many homes in Atlanta: 1 in 7792.
141 To make their case, the prosecution relied on only two of the twenty-eight suspected murders---the one from the river, Nathaniel Cater, and another recovered in the same general area a month before, Jimmy Ray Payne A single rayon fiber had been found on his shorts, which was consistent with the carpeting in Williams' station wagon. In this second case, statistical probability was also employed. With Chevrolet's help, the investigators determined that there was a 1 in 3,828 chance that Payne had acquired the fiber via random contact with a car that had this carpeting installed.
142 Math is good When the odds in both cases were multiplied, the law of probability that both men could have picked up these fibers in places other than Williams' home and car came out to 1 in almost 30,000,000. That seemed pretty staggering.
143 The prosecution also introduced into evidence the fibers found on the bodies of ten of the other victims (allowed in Georgia courts), which also matched those in Williams' car or home. These, they claimed, showed a pattern, and taken altogether, it increased the odds in the fiber evidence into numbers that no one could even comprehend. In total, there were 28 fiber types linked to Williams. In addition, several witnesses had come forward to place Williams with some of the victims, and others claimed to have seen suspicious scratches on Williams' arms.
144 After only twelve hours, the jury returned a guilty verdict, with two life sentences. The police announced that twenty-two of the unsolved murder cases were now closed, despite the fact that there was no real proof for those victims. Subsequently the Williams conviction has become controversial. To understand this, let's look at how fiber analysis is done.
145 Fiber Analysis Cross transfers of fiber often occur in cases in which there is person-to-person contact, and investigators hope that fiber traceable back to the offender can be found at the crime scene, as well as vice versa. Success in solving the crime often hinges on the ability to narrow the sources for the type of fiber found, as the prosecution did with their probability theory on the fibers in the Williams case.
146 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. For example, when fibers appeared to link two Ohio murders in the 1980s, it was just the start of building a case, but without the fibers, there would have been no link in the first place.
147 Kristen Lea Harrison In 1982, Kristen Lea Harrison was abducted from a ball field in Ohio and her body was found six days later some thirty miles away. She had been raped and strangled. Orange fibers in her hair looked suspiciously like those that had been found on a twelve-year-old female murder victim from eight months earlier in the same county. Since they were made of polyester and were oddly shaped (trilobal), forensic scientists surmised that it was carpet fiber. In addition, a box found near Kristin's body and plastic wrap around her feet indicated that the killer had once ordered a special kind of van seat, but then leads dried up.
148 Kristen Lea Harrison Some time later, a 28 year-old woman was abducted and held prisoner in a man's home. He tortured her and appeared to be intent on killing her. When he left, she escaped and reported him. Police noticed that he had a van similar to the one into which Kristin had been forced. It proved to have orange carpeting that matched the fibers in her hair. The color was unique, which allowed scientists to trace it to a manufacturer who supplied information about its limited run. Apparently only 74 yards of it had been shipped to that area of Ohio. That helped to narrow down possibilities. Other evidence established a more solid link and Robert Anthony Buell was eventually convicted.