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Forensic Science: Fundamentals & Investigations, Chapter 4 2
Introduction
o Fibers are used in forensic science to create a link between crime and suspect
o When fibers are transferred directly from victim to
suspect or suspect to victim, this is called: direct
transfer.
o Through normal activities
– We shed fibers
– We picked up fibers
o Very small fibers are classified as trace evidence
o Collecting fibers within 24 hours is critical
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Fiber Evidence
A fiber is the smallest unit of a textile material that has a length many times
greater than its diameter. A fiber can be spun with other fibers to form a yarn that
can be woven or knitted to form a fabric.
The type and length of fiber used, the type of spinning method, and the type of
fabric construction all affect the transfer of fibers and the significance of fiber
associations. This becomes very important when there is a possibility of fiber
transfer between a suspect and a victim during the commission of a crime.
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric3.htm#Fiber%20Evidence
Matching unique fibers on the clothing of a victim to fibers on a suspect’s clothing
can be very helpful to an investigation, whereas the matching of common fibers
such as white cotton or blue denim fibers would be less helpful.
The discovery of cross transfers and multiple fiber transfers between the suspect's
clothing and the victim's clothing dramatically increases the likelihood that these
two individuals had physical contact.
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Many different natural fibers that come from plants and animals are used in the
production of fabric. Natural plant fibers are produced by stems, leaves
seeds and fruits.
http://www.fireflydiapers.com/articles/diaperarticle_naturalfibersabsorb.htm
Cotton fibers are the plant fibers most commonly used
in textile materials Common polymer is cellulose.
Cotton has only one (1) seed.
The animal fiber most frequently used in the
production of textile materials is wool, and the most
common wool fibers originate from sheep.
Natural Fibers
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Images: http://www.trashforteaching.org/phpstore/product_images/YarnWS.JPG
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric3.htm#Fiber%20Evidence
http://www.jivepuppi.com/images/fiber_evidence.jpg
More than half of all fibers used in the production of
textile materials are synthetic or man-made.
Categorized as regenerated fibers and polymers.
Nylon, rayon, and polyester are all examples of synthetic
fibers.
Cross-section of a
man-made fiber
Synthetic Fibers
Fibers under a microscope
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Forensic Science: Fundamentals & Investigations, Chapter 4 6
How Forensic Scientists Use Fibers
Fiber evaluation can show
• Type of fiber
• Number of fibers
• Color
• Possibility of violence
• Location of suspects
• Point of origin
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How Fibers are collected by CSI team.
o tweezers
o special vacuums
o sticky tape
Forensic Science: Fundamentals & Investigations, Chapter 4 7
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Forensic Science: Fundamentals & Investigations, Chapter 4 8
Sampling and Testing
o Shedding—common form of fiber transfer
o Microscopes reveal characteristic shapes and markings
o Infrared spectroscopy reveals chemical structures to differentiate similar fibers
o Destructive Testing Methods
• Burning fibers
• Dissolving fibers in various liquids
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Forensic Science: Fundamentals & Investigations, Chapter 4 9
Sampling and Testing
Compare fibers found on different suspects with those found at the crime scene
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10
Fiber Type Burn Rate/Type Smell Smoke Product Left
Wool
Will not burn on it's
own, burns briefly and
Chars, shrinks away
from flame
Smells like burnt hair Little smoke
Black ash that
crumbles when
poked
CottonFlares into bright flame
and burns rapidly
Smells like burnt
paperLittle smoke Fine gray ash
Nylon
Burns out shortly after
removing from flame,
melts and burns away
Smells like celery Gray smoke
Cream colored
bead, bead
darkens if
PolyesterBurns out shortly after
removing from flame
Mild burnt plastic
smellBlack smoke
Melts and beads
into black mass
LinenFlares into bright flame
and burns rapidly
Smells like burnt
paperLittle smoke
Black ash that
crumbles when
poked
SilkDoesn't burn on own
for extended time
Mild smell, burnt or
charred meatLittle smoke
Black ash that
crumbles when
poked
Fiber Identification by Burning Test
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Forensic Science: Fundamentals & Investigations, Chapter 4 11
Fiber Classification —Natural Fibers
Animal fibers (made of proteins):
o Wool and cashmere from sheep
o Mohair from goats
o Angora from rabbits
o Hair from alpacas, llamas, and camels
o Silk from caterpillar cocoons(longer fiber does not shed easily)
woven wool
textile
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Forensic Science: Fundamentals & Investigations, Chapter 4 12
Fiber Classification —Natural Fibers
Plant fibers (made of the polymer cellulose):
o Absorb water
o Insoluble in water
o Very resistant to damage from harsh chemicals
o Dissolvable only by strong acids
o Becomes brittle over time
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Forensic Science: Fundamentals & Investigations, Chapter 4 13
Fiber Classification —Natural Fibers
Plant fibers:
o Cotton—most common textile plant fiber (picture) one (1) seed
o Coir from coconuts is durable
o Hemp, jute, and flax from stems grow in bundles
o Manila and sisal from leaves deteriorate more quickly
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Forensic Science: Fundamentals & Investigations, Chapter 4 14
Fiber Classification —Natural Fibers
Mineral Fibers:
o Fiberglass—a fibrous form of glass
o Asbestos—a crystalline structure
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Forensic Science: Fundamentals & Investigations, Chapter 4 15
Fiber Classification —Synthetic Fibers
o 50% of fabrics are artificially produced
o Examples:
• Rayon
• Acetate
• Nylon
• Acrylic
• Polyester
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Forensic Science: Fundamentals & Investigations, Chapter 4 16
Fiber Classification —Synthetic Cellulose Fibers
Regenerated Fibers (derived from cellulose or modified natural fibers) Add to notes
o Rayon– Most common in this group
– Imitates natural fibers, but stronger
o Celenese®
– Cellulose chemically combined with acetate
– Found in many carpets
o Polyamide nylon – Cellulose combined with three acetate units
– Breathable and lightweight
– Used in performance clothing
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Forensic Science: Fundamentals & Investigations, Chapter 4 17
Fiber Classification —Synthetic Polymer Fibers
Synthetic Polymer Fibers
o Petroleum base
o Very different from other fibers
o Monomers join to form polymers
o Fibers are spun together into yarns
o No internal structures
o Uniform diameters
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Forensic Science: Fundamentals & Investigations, Chapter 4 18
Fiber Classification—Synthetic Polymer Fibers
o Polyester• “Polar fleece”
• Wrinkle-resistant
• Not easily broken down by light or concentrated acid
• Added to natural fibers for strength
o Nylon• Easily broken down by light and concentrated acid
• Otherwise similar to polyester
spandex nylon
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Forensic Science: Fundamentals & Investigations, Chapter 4 19
Fiber Classification—Synthetic Polymer Fibers
o Acrylic
• Inexpensive
• Tends to “ball” easily
• Substitute for artificial wool or fur
o Olefins
• High performance
• Quick drying
• Resistant to wear
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Forensic Science: Fundamentals & Investigations, Chapter 4 20
Comparison of Natural and Synthetic Fibers
Visual Diagnostics of Some Common Textile Fibers
under Magnification
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Forensic Science: Fundamentals & Investigations, Chapter 4 21
Yarns, fabrics, and textiles
o Yarns—fibers (of any length, thick or thin, loose or tight) twisted or spun together
o Blending fibers meets different needs (e.g., resistance to wrinkling)
o Fibers are woven into fabrics or textiles
• Threads are arranged side by side (the warp)
• More threads (the weft) are woven back and forth crosswise through the warp
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Forensic Science: Fundamentals & Investigations, Chapter 4 22
Weave Patterns
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Forensic Science: Fundamentals & Investigations, Chapter 4 23
. . . . . . . . . . . . . Summary . . . .
o Fibers are a form of class evidence.
o Fibers are a form of trace evidence.
o Fibers are spun into yarns having specific characteristics.
o Yarns are woven, with different patterns, into clothing or textiles.
o Fiber evidence is gathered using different techniques.
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Forensic Science: Fundamentals & Investigations, Chapter 4 24
. . . . . . . . . . . . . . . . . Summary
o Fibers are analyzed using burn tests, tests for solubility in different solutions, polarized light microscopy, or infrared spectroscopy.
o Fibers are classified as natural or synthetic.
o Natural fiber sources include: • Animal hair
• Plant seeds, fruit, stems, or leaves
• Minerals.