FIBERS AND TEXTILES
Mr. Chapman – Forensics 30
What is a fiber?
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Fibers are used in forensic science to create a link
between a crime and a suspect.
Unlike fingerprints and DNA evidence, fibers are
not specific to a single person.
For example, a thief may own a jacket that matches
the type of fiber found at a crime scene. However,
that does not mean the thief was present at the
crime scene, as the jacket could belong to anyone.
Humans Shed?
When humans wear clothes, those
clothes shed fibers.
When you walk on a carpet, sit on a
couch, or pull on a sweater, fibers
can fall off or get picked up.
Forensic scientists look for these
small fibers in order to determine
where it is likely that a suspect has
been, although they never provide
actual proof. Why is this?
Criminals Try to be Sneaky
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Many criminals are aware of
some methods that investigators
try to use to identify them, such
as fingerprints and hair
samples.
As a result, these criminals often
wear gloves and hairnets.
However, many fibers are
extremely small and often go
unnoticed, and can provide
clear connections between
suspects and locations.
Fibers are Trace Evidence
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Fibers are a form of trace evidence. Recall that
trace evidence is any evidence that is left behind
from the contact of a person to an object or place.
Fibers originate from all sorts of objects, such as
carpets, clothing, linens, furniture, insulation, or rope.
Similar to hair, they may be transferred either by
direct transfer or also secondary transfer.
Direct vs. Secondary Transfer
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It is important in this study to remember the
difference between direct and secondary transfer.
Direct transfer occurs when fibers are transferred
directly from the suspect to the victim or vice versa.
Secondary transfer occurs when a victim picks up a
fiber from somewhere else and transfers it to the
suspect, or vice versa.
Early Collection of Fibers is Critical
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Within 24 hours, an estimated 95% of all fibers
may have fallen from a victim or been lost from a
crime scene.
Thorough examination of the victim and the crime
scene is required in order to get a fiber evidence.
Only fibers you would not expect to find on a victim
are investigated by CSIs.
Selection of Hair Samples
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CSIs will not examine fiber evidence that they
would expect to find on a victim.
For example, if a victim lived in a house that had
blue carpets and rugs everywhere, a CSI would not
examine a blue fiber they found on a victim.
Sketchy thought: If you are a killer, should you wear
colours that match your victims’ house?
How Forensic Scientists Use Fibers
Evidence of any kind must be evaluated, and this
is especially important for fibers, because they
are plentiful in the environment.
Unique Fibers are Most Useful
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Why do you think that a unique fiber is more useful
than a common one?
For example, white cotton is a much less valuable
fiber to find on a victim than an angora fiber.
Questions Scientists Ask Themselves About Fibers
Questions to Ask About Fiber...
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Type of fiber – what is the composition of the
fiber? How common or rare is it? What suspects or
victims or part of the crime scene had this type of
fiber on them?
Fiber color – Do the fibers from the suspect’s
clothes match the color found in the victim’s house?
Is the dye the same?
Questions to Ask About Fiber...
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Number of fibers found – How many fibers were
found – one or hundreds?
Where the fiber was found – How close can you
place the suspect to the scene of the crime – in the
house, or close to a victim’s body?
Textile the fiber originated from – Are these
carpet fibers, or upholstery from a car?
Questions to Ask About Fiber...
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Multiple Fiber Transfers – Is there only one type of
fiber transferred at the crime scene? Or are there
fibers from numerous sources from carpets and clothes
and bedding?
Type of crime committed- Ws the crime violent, a
break-and-enter, a kidnapping?
Time between crime and discovery of fiber – How
long ago did the transfer take place – an hour, a day,
or a week?
Sampling and Testing Fibers
How fiber evidence is gathered and tested.
How Fiber Evidence is Collected
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Fiber evidence is collected with three main tools:
Special Vacuums, Sticky Tape, and Forceps
Clearly, it is important to be very accurate in recording
where the fibers were found. Inaccurate documentation
may render the evidence useless in court.
What the Forensic Scientist Does
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Often, the forensic scientist will obtain small amount
of fibers from a crime scene, perhaps even just a
single fiber.
The first thing the scientist must do is identify the
type of fiber and its characteristics (such as colour
and shape). After that, the scientist must attempt to
match it to fibers from a suspect source, such as a
car or home.
Fibers Can be Precious
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Sometimes the forensic scientist
only has one fiber to work with.
When this is the case, the scientist
cannot do any tests that would
result in the destruction of the fiber,
since you would ruin your evidence
There are 2 methods of fiber
analysis that do not damage them
in any way.
Polarizing Light Microscopy
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Allows the scientist to look at the fiber using specific
wavelengths of light. The appearance of the fiber
under this type of microscope can tell the type of
fiber.
Natural fibers, like wool or cotton, only require an
ordinary microscope to see the distinguishing
characteristics.
Infrared Spectroscopy
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Emits a beam that bounces off the material and
returns to the instrument.
How the beam of light has changed reveals
something of the chemical structure of the fiber,
making it easy to tell the difference between fibers
that simply look alike.
Destructive Tests
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If many fibers are available, scientists can perform
tests on them that will ultimately destroy them.
Such tests include burning tests (also called flame
tests) and tests that involve dissolving the hair in
various substances.