Ch. 4
Fibers
Casey Anthony (fiber/duct tape) beginning and 6 ½ min in
Saferstein and Trace (several min in)
Fibers
The value of fibers as evidence depends
on narrowing their origin to a limited
number of sources.
 Fibers are a form of trace evidence that
is transferred between individuals and
objects during a crime- used to
corroborate other evidence that is found
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Important in these types of
cases:
Homicide
 Assault
 Sexual offense (transfer between
people)
 Hit and run (fibers adhere to vehicle)
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Types of Transfer
Direct Transfer: passes directly from
object to victim or vice-versa
 Secondary Transfer: transfer from a
source to a person then onto another
person
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Problems:
Mass production of our garments
 Need to calculate probabilities of how
many people would own that fiber
 Early collection is critical, w/in 24 hours
95% of all fibers will have fallen from
victim or lost from scene
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Types of Fibers: Natural
(depends on color and morphology)
1 . Animal
 Hair: Sheep, goats, camels, muskrat
(Use animal hair ID methods)
 Webbing: silk (from caterpillar cocoons)
llamas, alpacas, woven into textiles
 Fur: mink, rabbit, beaver
2. Plant
 Seed Fiber : Cotton cellulose(has ribbon
like twists at irregular intervals, Dyed
cotton provides more evidential value
than white cotton)
 Fruit Fiber: coir- fibers on coconut shell
(used for doormats, baskets)
 Stem Fiber – jute, hemp, flax (linen)
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Mineral Fiber – fiberglass, asbestos
Man-Made
Increase in amount since 1930’s
 1000’s of fibers under diff. Trademarks
 Get regenerated or synthetic
 Regenerated fibers: made from natural
raw materials (ex. Rayon cellulose &
nitric acid), made by forcing material thru
holes of spinnerets
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Synthetic Polymers
Synthetic man-made fibers
 Made thru polymerization
 Ex. Nylon (1st marketed synthetic
polymer), polyester, acrylics, olefins
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How is Polyester made?
Analyzing Fibers
Look at:
 Type of fiber
 Fiber color
 # of fibers found
 Where they were found,
 Textile it originated from
 Type of crime committed
 Time between crime and discovery of fibers
Types of Instruments Used:
Infrared Spectrophotometer- Measures
the quantity of radiation that a particular
material absorbs
 Microspectrophotometer Spectrophotometer w/ a light microscope
attached (get spectrum analysis also)1500x
 Polarizing Microscope -Study materials
that have double indices of refraction
(birefrigence)

Aspirin
Microspectrophotometer
Identification & Comparison of
Man-made fibers
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Fibers are class evidence, forensic
significance depends on location, number &
nature of fiber
Fabrics that can be exactly fitted together
are of obvious common origin
Common analysis: side by side
comparison of control and crime scene fiber
Color & diameter are obvious points of
comparison
Other Characteristics:
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Striations (lengthwise or surface)
Delustering agents (TiO2-reduces shine)
Cross section- see if unusually shaped
Weave Pattern - look at the warp/weft (plain,
basket, satin, twill, leno)
Dye composition- use microspectrophotometer
Chemical composition- see what broad class
of chemical it belongs to, use infrared
spectrophotometer
Polymeric structure (Ex. 200 samples of
acrylic fall into 24 diff. Groups)
 Physical properties: crystallinity,index of
refraction, birefringence, polarizing
properties, absorbance
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