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Fibers and Textiles. Fibers as Evidence. Fibers provide circumstantial or indirect evidence that can link a suspect to a crime scene Example: a thief may own a jacket that matches fibers found at a crime scene

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Fibers and Textiles


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    Presentation Transcript
    1. Fibers and Textiles

    2. Fibers as Evidence • Fibers provide circumstantial or indirect evidence that can link a suspect to a crime scene • Example: a thief may own a jacket that matches fibers found at a crime scene • Fibers are considered class evidencesince they are not specific to a single person • Most fibers are small or found in small amounts so they also are considered trace evidence

    3. Checkpoint • Classify fibers as… • Direct or circumstantial (indirect) evidence • Individual or class evidence

    4. Fibers as Evidence • Fibers may originate from carpets, clothing, linens, furniture, insulation, or rope ect… • Fibers naturally shed from these items • Fibers are easily transferred or “picked up” • Fibers may be transferred from a victim to a suspect, this is called direct transfer • Example: Fibers from victim’s sweater found on suspect • If fibers are picked by victim and then transferred to suspect it is called secondary transfer. • Example: Victim picks up fibers from his/her couch earlier in day and then transfers to the suspect later

    5. Checkpoint • Explain the difference between direct and secondary transfer

    6. Time is of Essence • Early collection of fibers in an investigation is critical • Within 24 hours an estimated 95% if all fibers may have fallen off a victim or been lost from a crime scene • Only fibers not expected to be found at a crime scene are investigated

    7. Something to Ponder • Police no longer cover dead bodies with cotton sheets at a crime scene. Why?

    8. The Value of Fibers • The value of fiber evidence in an crime investigation depends upon its potential uniqueness • Example: a white cotton fiber has less value than an orange wool fiber

    9. Not just Your Pets Shed! • Textile Shedding • The most common form of fiber transfer to be encountered is the shedding of a textile • Textile (fabric) = a flexible, flat material made by interlacing yarns • Clothing, carpets, upholstery ect… • Fibers are short are spun into yarn or threads, individual fibers can there be pulled away or shed from fabrics (textiles)

    10. Weave Pattern • Yarns and fibers are woven into textiles or fabrics • 5 Major types of weave pattern for textiles • Plain • Basket • Satin • Twill • Leno • Warp and Weft determines weave pattern • Warp = length wise fiber • Weft = crosswise (vertical fibers)

    11. Weave PatternsPLAIN • Plain • Alternating warp and weft pattern • Single fibers

    12. Weave PatternsBASKET • Basket • Alternating warp and weft pattern • Double fibers- 2 weft threads crossing to warp threads

    13. Weave PatternsSATIN • Satin • Wefts are woven over 3 or more warp threads at a time

    14. Weave PatternsTWILL • Twill • Weft is woven over 3 or more warps and then under one • Next row the pattern is shifted over one to the left or right by one warp thread

    15. Weave PatternsLENO • Leno • Use two warp threads and a double weft thread • To adjacent weft threads cross over each other

    16. Thread Count • Thread Count • In addition to weave pattern, textiles or fabrics also differ in thread count • Thread Count = threads per inch • Example- bed sheets • Often 180,200,400 or even 600 • Higher thread count = higher price

    17. Composition of Fibers • Fibers are polymers • Large molecules made of subunits or monomers • Plant fibers are made of cellulose • Cellulose is composed of glucose molecules linked together • Animal fibers are protein • Proteins are composed of amino acids linked together

    18. Fiber ClassificationNATURAL/ANIMALS • Animal Fibers • Wool = sheep • Cashmere and mohair = goats • Angora = rabbits • Silk = caterpillar Bombyxmori • Alpacas, llamas, camels

    19. Fiber ClassificationNATURAL/PLANTS • Plant fibers • Grouped by part of plant that they originate from • Seed • Fruit • Stem • Leaf ect… • Made of polymer cellulose which is made of glucose monomers • Absorbs water • Insoluble in water = does not dissolve in water • Resistant to damage from harsh chemicals • Fibers are usually 2-5 cm long • Become brittle over time • Often found as trace evidence at a crime scene

    20. Fiber ClassificationNATURUAL/PLANTS • Seed • Cotton • Made of cellulose • Easily woven and dyed • Used extensively in clothing and household textiles, most common type of fiber in world • Low in forensic value since it is so common • Fruit • Coir • Coarse fiber obtained from the covering of coconuts • Somewhat waterproof • Commonly used for doormats and baskets • Stem • Flax is most common, forms linen • Hemp and jute are also stem fibers • Leaf • Manila • Sisal- ropes and twines

    21. Fiber ClassificationNATURAL/MINERALS • Minerals-not made of proteins nor cellulose • Fiberglass • Short, very weak, and brittle fibers • Rolls of fiberglass are used for insulation • Asbestos • Long, thin, durable fibers • Used in building materials

    22. Synthetic FibersManufactured Fibers • Manufactured or regenerated fibers = cellulose or wood pulp is dissolved and cellulose is extracted. • Cellulose is then chemically combined with acetate and sent through tiny holes called spinnerets to make fibers that can be woven into yarn • Examples = rayon, celanese (carpets), capron (high performance clothing

    23. Synthetic FibersSynthetic Polymer Fibers • Synthetic Polymer Fibers • Petroleum (oil) based fibers, non-cellulose • No internal structures yet may be solid or hollow • Stronger than natural fibers • Examples: • Nylon • Polyester • Acrylic • olefins

    24. Collecting Fiber Evidence • Special vacuums • Sticky tape • forceps

    25. Sampling and Testing • Non destructive methods • Microspectrophotometry uses white light or infrared light and measures a fibers “true color by measuring wavelengths of light that are reflected • Polarized light- tool estimates reflective index (amount and angle of light reflected) of the fiber • Refractive index- uses light beams and measures degree in which light is bent as it travels through fiber • Scanning electron microscope- can scan the surface textiles or fabrics to examine how damage occurred

    26. Sampling and Testing • Destructive Methods • Burn tests • Dissolving in various solvents

    27. Burn Key