Fibers as Evidence
Another example of trace evidence
What is a Fiber?
 According to the FBI, a fiber is the
“smallest unit of a textile material that
has a length many times greater than its
diameter”.
 Fabric and fiber are NOT the same.
Fabric is the type of material and fibers
are the threads that are woven to create
the fabric.
The are two types of fibers:
natural and man-made (synthetic)
 Natural
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Cotton
Linen
Wool
Mohair
Cashmere
Silk
 Man-Made
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Polyester
Rayon
Nylon
Acetate
Acrylic
Spandex
Classification of Natural Fibers
 Natural fibers are classified based
on their origin. The three
classifications for natural fibers
are:
1. Vegetable/Plant
2. Animal
3. Mineral
Vegetable or Plant Fibers
 The most common plant fiber is cotton.
The wide-use of undyed white cotton in
clothing and other fabrics has made this
fiber meaningless as evidence.
However, when the cotton is dyed with a
combination of colors, the evidentiary
value is increased.
 Cotton fibers are ribbon-like and twist at
irregular intervals. This is a unique trait
for cotton.
A Microscopic Look at Cotton
Other Vegetable/Plant Fibers
include:
 Linen- made from the skin of the stem of
a flax plant. Linen fibers are used in
clothing, lace and bed sheets.
 Ramie, Jute and Hemp- also made from
the skin of a plant stem, but processed
differently from linen. These fibers are
mainly used for rope.
 Kapok- made from the seed pod of a
tropical tree. These fibers are used as
fillers for pillows, mattresses and toys.
A Microscopic Look at Linen,
Hemp and Kapok
Animal Fibers
 Animal fibers are the most common
natural fiber found at a crime scene.
These include: wool, mohair, cashmere,
alpaca and mink.
 The animal fiber that is most commonly
used in textile materials is wool. The
animal wool most commonly used is a
sheep. Wool is used for clothing and
carpet.
A Microscopic Look at Wool and
Cashmere. These are animal hairs so
you may notice the medulla and the
cuticle.
Animal Fibers from Excrement
 Silk comes from the
blind, flightless moth
Bombyx mori.
 After the silkworm
hatches, it eats
mulberry leaves
continuously for 6
weeks. Next, it
secretes a clear fluid
that hardens into a silk
cocoon. This cocoon is
separated into silk
fibers.
A Microscopic Look at Silk
 Silk has a
triangular structure
that causes the silk
fiber to refract
incoming light at
different angles.
This refraction
results in a
shimmering,
shining
appearance.
A Mineral Fiber
 Asbestos is a naturally occurring silicate
mineral that is composed of thin fibrous
crystals.
 Asbestos has been used in building
materials since the late 19th century.
 Asbestos has been identified as a
carcinogen so use of this material is
limited.
A Microscopic Look at
Asbestos
Man-Made/Manufactured
Fibers
 More than 50% of all
textiles are created
from man-made
fibers.
 Rayon, the first manmade fiber, was
created in 1911.
 Nylon (to the right)
followed in 1939.
Classification of Man-Made
Fibers
 Man-Made/Manufactured made be
classified into two groups:
 Regenerated
 Synthetic
Regenerated Fibers
Regenerated fibers are
manufactured from the cellulose
of natural raw materials. This
cellulose is chemically treated
and then forced through the
small holes of a spinning jet.
Regenerated fibers include: rayon
and acetate.
Creating Regenerated Fibers
Synthetic Fibers
 Most of the fibers manufactured today
are synthetic.
 Synthetic fibers are polymers or longchained molecules. Polymers exist in
numerous forms and varieties.
 The most common synthetic fibers are
nylon, polyester and acrylic.
 Nylon and polyester are the most
common of the man-made fibers.
Fibers as Evidence
 Fibers may be exchanged between two
objects or between an individual and an
object.
 Whether or not a fiber is transferred is
dependent on the type of fabric(s)
involved and the length of time of the
contact .
Fibers as Evidence (cont)
 The cross-section of
a man-made fiber is
manufacturer
specific. Some cross
sections are more
common than others.
Unusual cross
sections increase the
value of the
evidence.
Fibers as Evidence (cont)
 Fibers may be dyed before or after they
are woven into a fabric.
 Dye may also be applied to the surface
of a fabric.
 A dye’s color may be absorbed unevenly
and may fade over time.
 All of these factors must be considered
when trying to match a crime scene
sample with a control sample.
The Analysis of Fibers
A Microspectrophotometer compares fiber
colors through spectral patterns.
Chromatography gives a more detailed
analysis of the dye composition.
Double Refraction determines the value of the
refractive index of the fiber.
Infrared Spectrophotometry allows infrared
analysis of a single strand of fiber while
being viewed under the microscope
When the fibers become a
fabric
Fabrics are composed of individual fibers.
These fibers may be knitted, woven,
bonded, crocheted, felted, knotted or
laminated. Most are either woven or
knitted.
The method used to construct the fabric
will determine the amount of stretch,
absorbency, water repellence, softness
and durability. These characteristics are
unique to a fabric.
Woven Fabric
Woven fabrics are made by interlacing the warp (lengthwise
thread) and the weft (crosswise thread).
The warp runs the length of the fabric and parallel to the
selvage which is the edge of the fabric.
The weft crosses over and under the warp threads.
Types of weave patterns include:
 Plain
 Twill
 Satin
The Plain Weave
 Simplest and most
common weave
 Warp and weft pass
under each other
alternately
 Create even patterns
of 1/1 and 2/2
 Design resembles a
checkerboard
The Twill Weave
 Created by passing
the warp thread over
one to three weft
threads before going
under.
 Makes a diagonal
weave
 Design resembles a
stair step pattern
 Denim is the most
obvious example
The Satin Weave
 The interlacing is not
uniform
 Interlacing weave
passes over four or
more yarns
 Satin is the most
obvious example
Knitted Fabric
Knitted fabrics are
made by interlocking
loops into a specific
arrangement.
It may be one
continuous thread or
a combination of
threads.
The yarn is formed into
successive rows of
loops.
The Weave Pattern and
Transfer
 A tightly woven or knitted fabric “sheds” less
than a loosely woven or knitted fabric.
 Some textile materials such as leather do not
transfer fibrous material.
 The age and condition of the fabric will affect
the amount of fiber transfer.
 How often and for how long a fabric was
manufactured is also important to an
investigation.
Ripped Fabric
 If fabric evidence is ripped or torn, and
both pieces are collected, the edges will
be examined under a comparison
microscope. The weave pattern must
match.
Collection of Fiber Evidence
 Fibers that are visible and attached to an
object should be photographed, drawn
and described. Then the entire object
should be packaged.
 If fibers are visible and loose they should
be carefully removed with clean
tweezers and packaged in a paper
bindle.
Collection of Fiber Evidence
 If the investigator suspects that an object
has fiber evidence, but it is not visible to
the naked eye, the object will be sent to
the lab where tape will be used to collect
any loose fibers.
 If loose fibers are in a victim’s hair, the
hair should be combed over clean paper.
Collection of Fabric Evidence
 Bag fabric items individually in paper
bags.
 Make sure that different items are not
placed on the same surface before
being bagged.
The Wayne Williams Case
 The Wayne Williams case (pg. 100-110
in the textbook) was solely based on hair
and fiber evidence.
 The fibers were unique in color and
cross-sectional area.
 Williams continues to insist that he is
innocent.