Someone stole a CD and a portable CD player from the mall
music store. Shady Shrew claims he saw the stork unwrap
those items and immediately start listening to music. Slylock
Fox strongly suspects Shady's account is false. Why?
Source: http://www.slylockfox.com/arcade/BrainBogglers/index.html
Fiber Evidence
Fiber Evidence
A fiber is the smallest unit of a textile material that has a length many times
greater than its diameter.
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.
The discovery of cross transfers increases the likelihood that these two individuals
had physical contact.
Sampling and Testing
•
How are fibers collected?
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–
–
–
–
Special Vacuums
Sticky Tape
Forceps (tweezers)
Black Lights
Magnifying Glasses
Forensic Science:
Fundamentals & Investigations,
Chapter 4
4
Natural Fibers
Many different natural fibers that come from plants and animals are used in the
production of fabric.
Cotton fibers are the plant fibers most commonly used
in textile materials
The animal fiber most frequently used in the
production of textile materials is wool, and the most
common wool fibers originate from sheep.
http://www.fireflydiapers.com/articles/diaperarticle_naturalfibersabsorb.htm
Natural Fibers: Animal Fibers
• Sheep (wool)
• most common; the end use is often determined by
coarseness
• fine wool fibers are used for clothing, while coarse
wool fibers are used in carpeting
• Goat (mohair, cashmere)
• Camel (wool)
• Llama
• Alpaca (wool)
• Fur fibers from mink, rabbit, beaver, etc.
• Silk (fiber from the cocoon of the silkworm)
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Natural Fibers: Plant Fibers
• Cotton (ribbon-like shape with irregular twists; most common)
• Flax (Linen)
• Ramie
• Sisal (often used in linen rugs)
• Jute (used in ropes)
• Hemp (the common name for cannabis for industrial or nondrug use; typically used for rope or sack)
• Kapok (fiber from kapok tree seed pods; used in pillows and
mattress stuffing)
• Coir (coconut husks; used in carpet, rugs)
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Fiber Classification
—Natural Fibers
Plant fibers (made of the polymer cellulose):
• can absorb water.
• are insoluble in water.
• are very resistant to damage from harsh
chemicals.
• can only be dissolved by strong acids.
• can be common at crime scenes because
they become brittle over time.
Forensic Science:
Fundamentals & Investigations,
Chapter 4
8
Synthetic Fibers
More than half of all fibers used in the production of textile
materials are synthetic or man-made.
Nylon, rayon, and polyester are all examples of synthetic
fibers.
Cross-section of a
man-made fiber
Fibers under a microscope
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
Fiber Classification
—Synthetic (artificially produced) Fibers
• Until the nineteenth century only plant and
animal fibers were used to make clothes and
textiles.
• Half the products produced today are artificially
produced.
• Artificially produced fibers include rayon,
acetate, nylon, acrylics, and polyesters.
Forensic Science:
Fundamentals & Investigations,
Chapter 4
10
Federal Trade Commission Rules and Regulations Under the
Textile Products Identification Act, 1954
Generic names for manufactured fibers
•
•
•
•
•
•
•
•
•
Acetate
Acrylic
Anidex
Aramid
Glass
Lyocel
Nylon
Metallic
Modacrylic
•Novoloid
•Olefin
•Polyester
•Rayon
•Saran
•Spandex
•Vinal
•Vinyon
Synthetic Fibers
More than half of all fibers used in the production of textile
materials are manmade.
• Polyester (most common; wrinkle resistant; often spun
with cotton)
• Nylon (very common; elastic and strong; lustrous and
silk-like when stretched)
• Acrylics (wool-like, soft and warm; quick drying and
resistant to moths)
• Rayon (cellulose-derived, regenerated, thin fiber)
• Acetates (cellulosed-based, wrinkle-resistant fiber)
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Man-Made Fibers
• The cross section of a manmade fiber can be
manufacturer-specific
• Some cross sections are
more common than others,
and some shapes may only
be produced for a short
period of time.
• Unusual cross sections
encountered through
examination can add
increased significance to a
fiber association.
Cross-sectional views of nylon carpet
fibers as seen with a scanning electron
microscope (SEM)
Comparison of
Natural and
Synthetic Fibers
Visual Diagnostics of Some Common Textile Fibers
under Magnification
Forensic Science:
Fundamentals & Investigations,
Chapter 4
14
Forensic Fiber Analysis
Why would this information be valuable to a forensic
scientist?
• The world produced
approximately 80 billion
pounds of fabric in 1995,
about half of which was
cotton
• The other approximately
44 billion pounds of fiber
were manufactured or
synthetic.
Table 1.
U.S. Annual Production for Manufactured Fibers:
1995
(millions of pounds)
Fiber
Polyester
Product
3,887
Nylon
270
Olefin
521
Rayon/Acetate/Triace
tate
498
Acrylic/Modacrylic
432
(Table 1 [6]). All these fibers were used in a
variety of applications including but not
limited to clothing, household textiles,
carpeting, and industrial textiles.
Weaving
Lengthwise threads (the warp) are woven by crosswise threads
(the weft) in a pattern.
Common Weave Patterns
• Plain (firm, tends to wrinkle)
• Basket (not very durable, shrinks when
washed)
• Satin (not durable, shiny surface)
• Twill (very strong, dense and compact, soft)
• Leno (open weave, easily distorted)
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Agency 2011. All rights reserved.
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content used with permission.
Forensic Science:
Fundamentals & Investigations,
Chapter 4
17
Yarns, Fabrics, and Textiles
Weave Patterns
Forensic Science:
Fundamentals & Investigations,
Chapter 4
18
Fiber Comparisons
• Microscopic Comparisons
• Color
• Diameter
• Surface markings
•Cross-sectional shape
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Fiber Comparisons (continued)
• Polarized Light Microscopy – determines birefringence
(difference between two refractive indices) using polarized light
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Fiber Comparisons (continued)
• Fourier Transform Infrared Spectroscopy (FTIR) –
analysis of a fiber’s chemical composition based on its ability
to absorb light at different wavelengths
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Fiber Comparisons (continued)
• UV-Visible Microspectrophotometry – distinguishes
slight/subtle color differences based on absorption of light at
different wavelengths
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Introduction and How Forensic
Scientists Use Fibers
•
In an investigation, collection of fibers
within 24 hours is critical.
–
•
Why?
Fiber evaluation can show such things as the
type of fiber, its color, the possibility of
violence, location of suspects, and point of
origin.
Forensic Science:
Fundamentals & Investigations,
Chapter 4