2. Fibers
Objectives
You will understand:
Why fibers are class evidence.
How fibers can be used as circumstantial
evidence to link the victim, suspect,
and crime scene.
Why statistics are important
in determining the value of evidence.
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3. Fibers
Objectives, continued
You will be able to:
Distinguish and identify different types of
fibers.
Understand polymerization.
Carry out an experiment in thin-layer
chromatography.
Judge the probative value of fiber evidence.
Design and carry out scientific
investigations.
Use technology and mathematics to
improve investigations and
communications.
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4. Fibers
Fibers
Are considered class evidence
Have probative value
-common fibers, such as white
cotton and blue denim, have less
probative value
Are common trace evidence at a
crime scene
Can be characterized based on
comparison of both physical and
chemical properties
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5. Fibers
Trace Evidence Locard Principle
Can originate from Fibers can be left
linen, furniture, clothi behind and picked up
ng, carpet, insulation,
by suspect and/or
or rope
victim
The more fibers
collected from different Fibers are used to
parts of suspects, the create a LINK
easier it is to link the
suspect to the crime between suspect and
scene if all those fibers crime
are found
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6. Fibers
Direct Transfer Secondary Transfer
Fibers directly from Victim has fibers on
victim to suspect him that he/she
Fibers directly from picked up from
suspect to victim elsewhere and
transferred them to
suspect
Suspect picked up
fibers from elsewhere
and transferred the to
victim
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7. Fibers
Early Collection CRITICAL Example:
With in 24 hours, 95% may Would you
examine pink
have fallen from victim or been fibers on a
lost at a crime scene victim if she
Collect from scene and lived in a
house with
victims body (and any wall to wall
suspects if available) pink
carpeting?
Only fibers not expected to be
found at the scene are
investigated
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8. Fibers
Questions a Forensic Scientist Must Ask When Analyzing Fibers
Type of Fiber
Composition; common or rare; what suspect/victim/part of crime scene had fiber on them/it?
Fiber Color
Does color of suspects clothes match the color of the fiber found on victim/scene? Is it the same dye?
Number of Fibers Found
How many fibers—1 or 100?More fibers =possibly more violence/struggle or longer contact
Where the fiber was found
How close can you place suspect to the scene of the crime?
Textile the fiber originated from
From carpet, upholstery, car, etc.
Multiple Fiber transfers
Is there only one type or many different types at the scene? More sources suggest longer contact or possible violence.
Type of crime committed
Was it violent, breaking and entering , kidnapping? Each type of crime has expected pattern of contact between suspect, victim
and scene that is reflected in transfer of fibers.
Time between crime and discovery of the fiber
How long ago did transfer take place—an hour ago, a day, a week? Unless the fiber location is undisturbed, the value of the
fiber found is gradually reduced as time goes by (b/c fibers will be expected to fall off or fibers not related to crime can be
picked up)
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9. Fibers
Terms
Textile Yarns
Things like carpeting, Made up of fibers
clothing, upholstery that are spun together
Constructed by
weaving or
intertwining yarns
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10. Fibers
Fabric
Fabric is made of fibers. Fibers
are made of twisted
filaments.
Types of fibers and fabric:
Natural—animal, vegetable, or
inorganic
Artificial—synthesized or
created from altered
natural sources
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11. Fibers
Types of Fibers
Synthetic Natural
Rayon Silk
Nylon Cotton
Acetate Wool
Acrylic Mohair
Spandex Cashmere
Polyester
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12. Fibers
Classification
Natural fibers are classified
according to their origin:
1.)Plants/Vegetable or cellulose
- seeds, fruits, stems and
leaves
-cellulose (insoluble in
water)
-short (2-5 cm)
2.) Animal or protein
3.) Mineral
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13. Fibers
Cellulose Fibers
Cotton—vegetable fiber;
strong, tough, flexible, moisture-
absorbent, not shape-retentive
Rayon—chemically altered
cellulose; soft, lustrous, versatile
Cellulose acetate—cellulose that is
chemically altered to create an
entirely new compound not found
in nature
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14. Fibers
Fiber Comparison
Can you describe the difference(s) between the cotton on
the left and the rayon on the right?
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15. Fibers Animal
Fibers
3 sources
Hair
Brushed out of animals coat
Shed or clipped
Wool is most common animal hair used in textiles
Fur
Skin of animal treated, remains flexible and retains fur…found in coats and
gloves
Not a textile
Webbing
Ex. Silk
Collected from a cocoon of caterpillar Bombax mori
Fibers very long , they tend to not shed as easily as hair fibers
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16. Fibers
Protein Fibers
Wool—animal fiber coming most
often from sheep, but may be goat
(mohair), rabbit
(angora), camel, alpaca, llama, or
vicuña
Silk—insect fiber that is spun by a
silkworm to make its cocoon; the
fiber reflects light and has
insulating properties
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17. Fibers
Mineral Fibers ( come from rocks)
Asbestos—a natural fiber that has been used in fire-resistant
substances
Rock wool—a manufactured mineral fiber
Fiberglass—a manufactured inorganic fiber
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18. Fibers
Synthetic Fibers
Made from derivatives of petroleum, coal, and natural gas
Nylon—most durable of man-made fibers; extremely lightweight
Polyester—most widely used man-made fiber
Acrylic—provides warmth from a lightweight, soft, and resilient
fiber
Spandex—extreme elastic properties
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19. Fibers
Fabric Production
Fabrics are composed of individual threads or yarns that are made of
fibers and are knitted, woven, bonded, crocheted, felted, knotted, or
laminated. Most are either woven or knitted. The degree of
stretch, absorbency, water repellence, softness, and durability are all
individual qualities of the different fabrics.
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20. Fibers
Weave Terminology
Yarn—a continuous strand of fibers or filaments that may be twisted
together
Warp—lengthwise yarn
Weft—crosswise yarn
Blend—a fabric made up of two or
more different types of fibers
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22. Fibers
Plain Weave
The simplest and most common weave
pattern
The warp and weft yarns pass under
each other alternately
Design resembles a checkerboard
Characteristics:
Firm and wears well
Snag resistant
Low tear strength
Tends to wrinkle
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23. Fibers
Twill Weave
The warp yarn is passed over one to three
weft yarns before going under one.
Makes a diagonal weave pattern.
Design resembles stair steps.
Denim is one of the most common
examples.
Characteristics:
Very strong
dense and compact
different faces;
diagonal design on surface
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24. Fibers
Satin Weave
The yarn interlacing is not uniform
Creates long floats
Interlacing weave passes over four or
more yarns
Satin is the most obvious example
Characteristics:
Not durable
Tends to snag and break during wear
Shiny surface
Little friction with other garments
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25. Fibers
Basket
Alternating pattern of two weft threads
crossing two warp threads
Characteristics:
Does not wrinkle
Open, porous weave
Not very durable
Shrinks when washed
Tends to distort as yarn shifts
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26. Fibers
Leno
This uses two warp threads and a double weft thread
The two adjacent warp threads cross over one
another.
The weft travels left to right and is woven between
the two warp threads
Characteristics:
Open weave
Easily distorted with wear and washing
Stretches in one direction
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27. Fibers
Knitted Fabric
Knitted fabrics are made by
interlocking loops into a specific
arrangement.
It may be one continuous thread or a
combination.
Either way, the yarn is formed into
successive rows of loops and then
drawn through another series of
loops to make the fabric.
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28. Fibers
Polymers
Synthetic fibers are made of polymers, which are long chains of
repeating chemical units.
The word polymer means many (poly) units (mer).
The repeating units of a polymer are called monomers.
By varying the chemical structure of the monomers or by varying the
way they are joined together, polymers are created that have
different properties.
As a result of these differences, they can be distinguished from one
another forensically.
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29. Fibers
Filament Cross Sections
Round 4-lobed
Octalobal
Trilobal
Irregular
Dogbone or Multi-lobed
Dumbbell or Serrate
Synthetic fibers are forced out of a nozzle when they are hot, and then
they are woven. The holes of the nozzle are not necessarily round;
therefore, the fiber filament may have a unique shape in cross
section.
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30. Fibers
Testing for Identification
Microscopic observation
Burning—observation of how a
fiber burns, the odor, color of
flame, color of smoke, and the
appearance of the residue
Thermal decomposition—gently
heating to break down the fiber
to the basic monomers
Chemical tests—solubility and
decomposition
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31. Fibers
Testing for Identification
Density—the mass of an object
divided by the volume of the
object
Refractive index—measurement
of the bending of light as it
passes from air into a solid or
liquid
Fluorescence—absorption and
reemission of light; used for
comparing fibers as well as
spotting fibers for collection
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32. Fibers
Using Density
1 cc = 1 cm3 =1 mL
D= mass/ vloume…. Measured using “g/cc”
Used to confirm a fiber
Useful for single fibers and are non-destructive
Use columns with specific liquids to analyze
density
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34. Fibers
Dyes
Components that make up dyes can
be separated and matched to an
unknown.
There are more than 7,000 different
dye formulations.
Chromatography is used to separate
dyes for comparative analysis.
The way a fabric accepts a particular
dye may also be used to identify
and compare samples.
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35. Fibers
Collection of Fiber Evidence
Bag clothing items individually in paper bags. Make sure that different
items are not placed on the same surface before being bagged.
Make tape lifts of exposed skin areas and any inanimate objects.
Removed fibers should be folded into a small sheet of paper and stored
in a paper bag.
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36. Fibers
Fiber Evidence
Fiber evidence in court cases can be
used to connect the suspect to the
victim or to the crime scene. In the
case of Wayne Williams, fibers
weighed heavily on the outcome of
the case. Williams was convicted in
1982 based on carpet fibers that
were found in his home, in his
car, and on several murder victims.
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37. Fibers
More about Fibers
For additional information about fibers and other trace evidence, check out
truTV’s Crime Library at:
www.crimelibrary.com/criminal_mind/forensics/trace/1.html
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