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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.

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Presentation on theme: "Fibers and Textiles. Fibers as Evidence Fibers provide circumstantial or indirect evidence that can link a suspect to a crime scene – Example: a thief."— 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 evidence since 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 Patterns PLAIN Plain – Alternating warp and weft pattern Single fibers

12 Weave Patterns BASKET Basket – Alternating warp and weft pattern Double fibers- 2 weft threads crossing to warp threads

13 Weave Patterns SATIN Satin – Wefts are woven over 3 or more warp threads at a time

14 Weave Patterns TWILL 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 Patterns LENO Leno – Use two warp threads and a double weft thread – To adjacent weft threads cross over each other

16 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 Classification NATURAL/ANIMALS Animal Fibers – Wool = sheep – Cashmere and mohair = goats – Angora = rabbits – Silk = caterpillar Bombyx mori – Alpacas, llamas, camels

19 Fiber Classification NATURAL/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 Classification NATURUAL/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 Classification NATURAL/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 Fibers Manufactured 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 Fibers Synthetic 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 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

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