Chapter 4 Fibers Wherever he steps whatever he
Chapter 4: 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
Fibers Students will learn: The student will learn: § § § Chapter 6 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 1
Fibers Students will be able to: § § § Chapter 6 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 2
Fiber Identification " Who was Wayne Williams? " How was he convicted? (What evidence) Chapter 6 Kendall/Hunt Publishing Company 3
" " " " " Chapter 6 NCJRS Abstract The document referenced below is part of the NCJRS Library collection. To conduct further searches of the collection, visit the NCJRS NCJ Number: NCJ 093717 Title: Fiber Evidence and the Wayne Williams Trial, Part I Journal: FBI Law Enforcement Bulletin Volume: 53 Issue: 3 Dated: (March 1984) Pages: 12 -20 Annotation: The trial of Wayne Williams illustrates the use and importance of fiber evidence in a trial situation. Abstract: In 1982, a court in Georgia found Wayne Williams guilty of murder. An essential part of the case involved the association of fibrous debris removed from the bodies of 12 murder victims with objects from Williams's everyday environment. Although fiber evidence has often been an important part of criminal cases, the Williams trial differed from other cases in several important ways: fiber evidence was used to associate Williams with a large number of victims, fiber evidence was the main evidence, and the case received more publicity than most. Since all people are closely associated with items containing fibrous materials, the transference of textile fibers comes into play in many different types of criminal activity. When it is important to show that contact has taken place, textile fiber evidence can be invaluable. A forensic examiner must determine that a questioned fiber is similar to, or the same as, fibers in the composition of a particular object. The fiber examiner must compare various characteristics and properties which can be observed and/or determined. In addition, many scientific techniques are available for the examination and comparison of these properties. Once it has been determined that there is a fiber match, the significance of the resulting association depends considerably upon whether the fiber type is uncommon or unusual. Collection of fibrous materials from the scene of a crime, from a body, or from any other relevant setting is very important. 4
Fibers § § Chapter 6 Are considered class evidence Have probative value Are common trace evidence at a crime scene ( What are other examples of trace evidence? ) Can be characterized based on comparison of both physical and chemical properties Kendall/Hunt Publishing Company 5
Fibers "Why is it so important to collect trace evidence as soon as possible? "How should fibers be collected at a crime scene? Chapter 6 Kendall/Hunt Publishing Company 6
Collect some fibers " Use tape, a sheet of notebook paper, and your own clothing " Work in groups of 3 or 4 " Press the tape against your clothing, peel it off to lift fibers, Put tape on sheet of paper. Use pants, sweaters, t-shirts, etc. . ) " Label each sample, (person, clothing, known label, etc…) take at least two samples person " Compare using a hand lens " Write a 1 page summary of results, which were alike, different, describe how they look, etc… Chapter 6 Kendall/Hunt Publishing Company 7
Collection of Fiber Evidence Chapter 6 § 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. § Why might cotton have lower probative value than other fibers? Kendall/Hunt Publishing Company 8
Collecting Fiber Evidence Chapter 6 § After 24 hours, 95% of trace evidence may be gone, (80 % gone after just 4 hours) § Lift with tape or with vacuuming § 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 9
Testing for Identification Chapter 6 § Microscopic observation § Birefringence– light passes through fiber and is refracted twice, emerges as two different wavelengths of polarized light § 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 10
Testing for Identification Chapter 6 § Density—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 § Microspectrophotometry– process allows you to see “true” color of a fiber or hair Kendall/Hunt Publishing Company 11
Identification and Comparison of Fibers Chapter 6 § Fourier 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 12
How are fibers classified? Chapter 6 Kendall/Hunt Publishing Company 13
Fabric § § Chapter 6 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 A) Manufactured or B) synthetic are two types of Artificial fibers Kendall/Hunt Publishing Company 14
Fabric " Manufactured fibers- rayon, acetate, triacetate; raw cotton or wood pulp are dissolved, the cellulose is extracted and regenerated in to fibers " Synthetic fibers- nylon, polyester; come from polymers Chapter 6 Kendall/Hunt Publishing Company 15
Types of Fibers Artificial (Manufactured and synthetic) § § § Rayon Nylon Acetate Acrylic Spandex Polyester Natural § § § § Chapter 6 Silk Cotton Woolsheep/goat/rabbit Mohair-angora goat Cashmeregoat/wool Flax (linen)-sheets Jute-twine/rope Kendall/Hunt Publishing Company 16
Classification Natural fibers are classified according to their origin: § Vegetable or cellulose § Animal or protein § Mineral Chapter 6 Kendall/Hunt Publishing Company 17
Cellulose Fibers " Cotton—vegetable fiber; strong, tough, flexible, moisture absorbent, not shape retentive, most common, twisted ribbon pattern " Rayon—chemically-altered lustrous, versatile " Chapter 6 cellulose; soft, Cellulose acetate—cellulose chemicallyaltered to create an entirely new compound not found in nature. Kendall/Hunt Publishing Company 18
Fiber Comparison Can you tell the difference(s) between the cotton on the left and the rayon on the right? Chapter 6 Kendall/Hunt Publishing Company 19
Protein Fibers Chapter 6 § Wool—animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama § 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 20
Mineral Fibers Chapter 6 § 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 21
Synthetic Fibers (Made from derivatives of petroleum, coal and natural gas) Chapter 6 § Nylon—most durable of man-made fibers; extremely light weight § Polyester—most widely used manmade fiber § Acrylic—provides warmth from a lightweight, soft and resilient fiber § Spandex—extreme elastic properties Kendall/Hunt Publishing Company 22
Fabric Production Fabrics are composed of individual threads or yarns, made of fibers, that are knitted, woven, bonded, crocheted, felted, knotted or laminated. ü Most are either woven or knitted. ü The degree of stretch, absorbency, water repellence, softness and durability are all individual qualities of the different fabrics. ü Chapter 6 Kendall/Hunt Publishing Company 23
Weave Terminology Chapter 6 § 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 24
Weave Patterns Thread count refers to the number of horizontal and vertical threads per square inch. Generally, the higher the thread count, the softer the sheet, and the more likely it will wear well-or even soften-over time. Good sheets range anywhere from 200 to 800, although you'll occasionally see numbers over 1, 000. Chapter 6 Kendall/Hunt Publishing Company 25
Plain Weave Chapter 6 § 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 26
Twill Weave Chapter 6 § 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 27
Satin Weave Chapter 6 § 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 28
Knitted 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. Chapter 6 Kendall/Hunt Publishing Company 29
Polymers Chapter 6 § 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 30
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. Chapter 6 Kendall/Hunt Publishing Company 31
Dyes Chapter 6 § 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 32
More about Fibers For additional information about fibers and other trace evidence, check out Court TV’s Crime Library at: www. crimelibrary. com/criminal_mind/forensics/trace/1. html Chapter 6 Kendall/Hunt Publishing Company 33
- Slides: 34