Fibers as Evidence

1
Fibers as Evidence

• Another example of trace evidence

2
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.

3
The are two types of fibers natural and man-made
(synthetic)

• Natural
• Cotton
• Linen
• Wool
• Mohair
• Cashmere
• Silk

• Man-Made
• Polyester
• Rayon
• Nylon
• Acetate
• Acrylic
• Spandex

4
Classification of Natural Fibers

• Natural fibers are classified based on their
  origin. The three classifications for natural
  fibers are
• Vegetable/Plant
• Animal
• Mineral

5
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.

6
A Microscopic Look at Cotton
7
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.

8
A Microscopic Look at Linen, Hemp and Kapok
9
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.

10
A Microscopic Look at Wool and Cashmere. These
are animal hairs so you may notice the medulla
and the cuticle.
11
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.

12
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.

13
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.

14
A Microscopic Look at Asbestos
15
Man-Made/Manufactured Fibers

• More than 50 of all textiles are created from
  man-made fibers.
• Rayon, the first man-made fiber, was created in
  1911.
• Nylon (to the right) followed in 1939.

16
Classification of Man-Made Fibers

• Man-Made/Manufactured made be classified into two
  groups
• Regenerated
• Synthetic

17
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.

18
Creating Regenerated Fibers
19
Synthetic Fibers

• Most of the fibers manufactured today are
  synthetic.
• Synthetic fibers are polymers or long-chained
  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.

20
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 .

21
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.

22
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 dyes 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.

23
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

24
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.

25
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

26
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

27
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

28
The Satin Weave

• The interlacing is not uniform
• Interlacing weave passes over four or more yarns
• Satin is the most obvious example

29
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.

30
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.

31
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.

32
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.

33
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 victims hair, the hair
  should be combed over clean paper.

34
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.

35
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.