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• 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

Checkpoint

• Classify fibers as…– Direct or circumstantial (indirect) evidence– Individual or class evidence

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

Checkpoint

• Explain the difference between direct and secondary transfer

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

Something to Ponder

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

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

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)

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)

Weave PatternsPLAIN

• Plain– Alternating warp and weft pattern• Single fibers

Weave PatternsBASKET

• Basket– Alternating warp and weft pattern• Double fibers- 2 weft threads crossing to warp threads

Weave PatternsSATIN

• Satin– Wefts are woven over 3 or more warp threads at a

time

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

Weave PatternsLENO

• Leno– Use two warp threads and a double weft thread– To adjacent weft threads cross over each other

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

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

Fiber ClassificationNATURAL/ANIMALS

• Animal Fibers– Wool = sheep– Cashmere and mohair = goats– Angora = rabbits– Silk = caterpillar Bombyx mori– Alpacas, llamas, camels

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

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

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

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

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

Collecting Fiber Evidence

• Special vacuums• Sticky tape• forceps

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

Sampling and Testing

• Destructive Methods– Burn tests– Dissolving in various solvents

Burn Key