Fibers

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Fibers

  1. 1. Fibers
  2. 2. FibersObjectives You will understand: Why fibers are class evidence. How fibers can be used as circumstantial evidence to link the victim, suspect, and crime scene. Why statistics are important in determining the value of evidence. Kendall/Hunt Publishing Company 22
  3. 3. FibersObjectives, continued You 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 33
  4. 4. FibersFibersAre considered class evidenceHave probative value -common fibers, such as white cotton and blue denim, have less probative valueAre common trace evidence at a crime sceneCan be characterized based on comparison of both physical and chemical properties Kendall/Hunt Publishing Company 44
  5. 5. Fibers Trace Evidence  Locard Principle  Can originate from  Fibers can be left linen, furniture, clothi behind and picked up ng, carpet, insulation, by suspect and/or or rope victim The more fibers collected from different  Fibers are used to parts of suspects, the create a LINK easier it is to link the suspect to the crime between suspect and scene if all those fibers crime are found Kendall/Hunt Publishing Company 55
  6. 6. Fibers Direct Transfer  Secondary Transfer  Fibers directly from  Victim has fibers on victim to suspect him that he/she  Fibers directly from picked up from suspect to victim elsewhere and transferred them to suspect  Suspect picked up fibers from elsewhere and transferred the to victim Kendall/Hunt Publishing Company 66
  7. 7. Fibers Early Collection CRITICAL  Example:  With in 24 hours, 95% may  Would you examine pink have fallen from victim or been fibers on a lost at a crime scene victim if she Collect from scene and lived in a house with victims body (and any wall to wall suspects if available) pink carpeting? Only fibers not expected to be found at the scene are investigated Kendall/Hunt Publishing Company 77
  8. 8. Fibers Questions a Forensic Scientist Must Ask When Analyzing Fibers Type of Fiber  Composition; common or rare; what suspect/victim/part of crime scene had fiber on them/it? Fiber Color  Does color of suspects clothes match the color of the fiber found on victim/scene? Is it the same dye? Number of Fibers Found  How many fibers—1 or 100?More fibers =possibly more violence/struggle or longer contact Where the fiber was found  How close can you place suspect to the scene of the crime? Textile the fiber originated from  From carpet, upholstery, car, etc. Multiple Fiber transfers  Is there only one type or many different types at the scene? More sources suggest longer contact or possible violence. Type of crime committed  Was it violent, breaking and entering , kidnapping? Each type of crime has expected pattern of contact between suspect, victim and scene that is reflected in transfer of fibers. Time between crime and discovery of the fiber  How long ago did transfer take place—an hour ago, a day, a week? Unless the fiber location is undisturbed, the value of the fiber found is gradually reduced as time goes by (b/c fibers will be expected to fall off or fibers not related to crime can be picked up) 88
  9. 9. Fibers Terms Textile  Yarns  Things like carpeting,  Made up of fibers clothing, upholstery that are spun together  Constructed by weaving or intertwining yarns Kendall/Hunt Publishing Company 99
  10. 10. FibersFabricFabric 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 1010
  11. 11. FibersTypes of FibersSynthetic Natural Rayon Silk Nylon Cotton Acetate Wool Acrylic Mohair Spandex Cashmere Polyester Kendall/Hunt Publishing Company 1111
  12. 12. FibersClassificationNatural fibers are classifiedaccording to their origin: 1.)Plants/Vegetable or cellulose - seeds, fruits, stems and leaves -cellulose (insoluble in water) -short (2-5 cm) 2.) Animal or protein 3.) Mineral Kendall/Hunt Publishing Company 1212
  13. 13. FibersCellulose FibersCotton—vegetable fiber; strong, tough, flexible, moisture- absorbent, not shape-retentiveRayon—chemically altered cellulose; soft, lustrous, versatileCellulose acetate—cellulose that is chemically altered to create an entirely new compound not found in nature Kendall/Hunt Publishing Company 1313
  14. 14. FibersFiber Comparison Can you describe the difference(s) between the cotton on the left and the rayon on the right? Kendall/Hunt Publishing Company 1414
  15. 15. Fibers Animal Fibers 3 sources  Hair  Brushed out of animals coat  Shed or clipped  Wool is most common animal hair used in textiles  Fur  Skin of animal treated, remains flexible and retains fur…found in coats and gloves  Not a textile  Webbing  Ex. Silk  Collected from a cocoon of caterpillar Bombax mori  Fibers very long , they tend to not shed as easily as hair fibers Kendall/Hunt Publishing Company 1515
  16. 16. FibersProtein FibersWool—animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama, or vicuñaSilk—insect fiber that is spun by a silkworm to make its cocoon; the fiber reflects light and has insulating properties Kendall/Hunt Publishing Company 1616
  17. 17. FibersMineral Fibers ( come from rocks)Asbestos—a natural fiber that has been used in fire-resistant substancesRock wool—a manufactured mineral fiberFiberglass—a manufactured inorganic fiber Kendall/Hunt Publishing Company 1717
  18. 18. FibersSynthetic FibersMade from derivatives of petroleum, coal, and natural gasNylon—most durable of man-made fibers; extremely lightweightPolyester—most widely used man-made fiberAcrylic—provides warmth from a lightweight, soft, and resilient fiberSpandex—extreme elastic properties Kendall/Hunt Publishing Company 1818
  19. 19. FibersFabric ProductionFabrics are composed of individual threads or yarns that are made offibers and are knitted, woven, bonded, crocheted, felted, knotted, orlaminated. Most are either woven or knitted. The degree ofstretch, absorbency, water repellence, softness, and durability are allindividual qualities of the different fabrics. Kendall/Hunt Publishing Company 1919
  20. 20. FibersWeave TerminologyYarn—a continuous strand of fibers or filaments that may be twisted togetherWarp—lengthwise yarnWeft—crosswise yarnBlend—a fabric made up of two or more different types of fibers Kendall/Hunt Publishing Company 2020
  21. 21. FibersWeave Patterns•Basket•Leno Kendall/Hunt Publishing Company 2121
  22. 22. FibersPlain WeaveThe simplest and most common weave patternThe warp and weft yarns pass under each other alternatelyDesign resembles a checkerboardCharacteristics:Firm and wears wellSnag resistantLow tear strengthTends to wrinkle Kendall/Hunt Publishing Company 2222
  23. 23. Fibers Twill WeaveThe 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.Characteristics: Very strong dense and compact different faces; diagonal design on surface Kendall/Hunt Publishing Company 2323
  24. 24. FibersSatin WeaveThe yarn interlacing is not uniformCreates long floatsInterlacing weave passes over four or more yarnsSatin is the most obvious exampleCharacteristics:Not durableTends to snag and break during wearShiny surfaceLittle friction with other garments Kendall/Hunt Publishing Company 2424
  25. 25. Fibers Basket Alternating pattern of two weft threads crossing two warp threads Characteristics:  Does not wrinkle  Open, porous weave  Not very durable  Shrinks when washed  Tends to distort as yarn shifts Kendall/Hunt Publishing Company 2525
  26. 26. Fibers Leno This uses two warp threads and a double weft thread The two adjacent warp threads cross over one another. The weft travels left to right and is woven between the two warp threads Characteristics:  Open weave  Easily distorted with wear and washing  Stretches in one direction Kendall/Hunt Publishing Company 2626
  27. 27. FibersKnitted FabricKnitted fabrics are made byinterlocking loops into a specificarrangement.It may be one continuous thread or acombination.Either way, the yarn is formed intosuccessive rows of loops and thendrawn through another series ofloops to make the fabric. Kendall/Hunt Publishing Company 2727
  28. 28. FibersPolymersSynthetic 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, they can be distinguished from one another forensically. Kendall/Hunt Publishing Company 2828
  29. 29. FibersFilament Cross Sections Round 4-lobed Octalobal Trilobal Irregular Dogbone or Multi-lobed Dumbbell or SerrateSynthetic fibers are forced out of a nozzle when they are hot, and thenthey are woven. The holes of the nozzle are not necessarily round;therefore, the fiber filament may have a unique shape in crosssection. Kendall/Hunt Publishing Company 2929
  30. 30. FibersTesting for IdentificationMicroscopic observationBurning—observation of how a fiber burns, the odor, color of flame, color of smoke, and the appearance of the residueThermal decomposition—gently heating to break down the fiber to the basic monomersChemical tests—solubility and decomposition Kendall/Hunt Publishing Company 3030
  31. 31. FibersTesting for IdentificationDensity—the mass of an object divided by the volume of the objectRefractive index—measurement of the bending of light as it passes from air into a solid or liquidFluorescence—absorption and reemission of light; used for comparing fibers as well as spotting fibers for collection Kendall/Hunt Publishing Company 3131
  32. 32. FibersUsing Density 1 cc = 1 cm3 =1 mL D= mass/ vloume…. Measured using “g/cc” Used to confirm a fiber Useful for single fibers and are non-destructive Use columns with specific liquids to analyze density Kendall/Hunt Publishing Company 3232
  33. 33. FibersUsing Refractive Index Kendall/Hunt Publishing Company 3333
  34. 34. FibersDyesComponents that make up dyes can be separated and matched to an unknown.There are more than 7,000 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 3434
  35. 35. FibersCollection 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 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 3535
  36. 36. FibersFiber EvidenceFiber evidence in court cases can beused to connect the suspect to thevictim or to the crime scene. In thecase of Wayne Williams, fibersweighed heavily on the outcome ofthe case. Williams was convicted in1982 based on carpet fibers thatwere found in his home, in hiscar, and on several murder victims. Kendall/Hunt Publishing Company 3636
  37. 37. FibersMore about FibersFor additional information about fibers and other trace evidence, check outtruTV’s Crime Library at:www.crimelibrary.com/criminal_mind/forensics/trace/1.html Kendall/Hunt Publishing Company 3737

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