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
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•
•
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Plain
Basket
Satin
Twill
Leno
– Warp and Weft determines weave pattern
» Warp = length wise fiber
» Weft = crosswise (vertical fibers)
Weave Patterns
PLAIN
• Plain
– Alternating warp and weft pattern
• Single fibers
Weave Patterns
BASKET
• Basket
– Alternating warp and weft pattern
• Double fibers- 2 weft threads crossing to warp threads
Weave Patterns
SATIN
• Satin
– Wefts are woven over 3 or more warp threads at a
time
• Twill
Weave Patterns
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 Patterns
LENO
• 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 Classification
NATURAL/ANIMALS
• Animal Fibers
– Wool = sheep
– Cashmere and mohair = goats
– Angora = rabbits
– Silk = caterpillar Bombyx mori
– Alpacas, llamas, camels
Fiber Classification
NATURAL/PLANTS
• Plant fibers
– Grouped by part of plant that they originate from
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•
•
•
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 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
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
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
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:
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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