EVIDENCE found at the Crime Scene

Report
Hair and Fiber Evidence
Trace evidence is small pieces of evidence left
behind at a crime
 Locard recognized the usefulness of trace
evidence in reconstructing crime scene as he is
known to say “EVERY CONTACT LEAVES A TRACE”
 Examples of Trace Evidence
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Hair
Fibers
The focus of our trace
evidence lessons
Soil
Paint
Glass
Writing samples
Gun shot residue, explosives, drugs
A
wide variety of
crimes leave hair
samples at the crime
scene
 Morphology CANNOT
link hair to a single
individual
 However, it can be used as strong corroborative
evidence placing an individual at a crime scene.
 Hair is very stable evidence and is resistant to
chemical decomposition, retaining structural
features over a long period of time
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Cuticle
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Outside covering on hair
Scale pattern is a useful
CLASS characteristic
The variety of patterns
formed by animal hair
makes it important in
species identification
Imbricate – found in all
human hairs and some
animals
Coronal –hair of small
rodents (mouse, rats)
and bats
Spinous – hair of minks,
seals, and cats
 Cortex
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Pigment granules
are in this section
of the hair
Color, shape, and
distribution of these
granules provide the
criminalist with
important points of
comparison among
the hairs of
different individuals
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Medulla
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Looks like a central canal
running through the hair
In many animals, the medulla
can be very wide, occupying
more than half the hair’s
diameter
For humans, the medulla usually
less than 1/3 of the diameter
Its important to note that
medulla can even vary between
hairs on a single individual
Medulla patterns vary greatly
with different animals (cat
medulla resembles a strand of
pearls and deer medulla looks
like spherical cells occupying
the entire center of the hair
strand
Unisereal – cat or rabbit
Lattice- deer, elk, goat
Vacuolated – dog, red fox, cattle
Multisereal – rabbit, chinchilla
Amorphous – human
continuous – black hair
fragmented – all other hair
 Various
medulla
patterns appear in
different species
of animals
Rounded root – hair lost naturally
Follicle attached – hair pulled out
Spade shaped root – most likely dog
Frayed root – most likely cat
Blackened Root – hair lost after death
Wine-glass shaped root – most likely deer
 Types
Natural fibers
(animal or plant)
 Man-made fibers
 Synthetic fibers
 Polymers
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Fibers are spun into yarn which can then be knitted
or woven into fabrics
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Fibers left at the crime scene can be matched
by class characteristics to fibers relating to the
suspect
It is more likely to be able to find a fiber (or
hair) on a piece of evidence or known source
that is immobile
Fibers may come from wigs, carpet, drapery,
furniture, blankets, etc.
The more fibers found, the more likely that
the evidence made direct contact with the
source of the fibers
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The fewer number of possible sources, the
more evidentiary value they have
Databases with fibers exists to compare
unknown samples to
When comparing fibers, analysts are comparing
the type of fiber, the way it was woven, and its
color
While billions of tons of fabric are produced,
duplicating the fiber/yarn and its exact color
are not too likely
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Derived entirely from animal or plant
sources
Wool – sheep (most common animal
fiber)
Cashmere – goats
Fur fibers such as mink, rabbit, beaver
and muskrat
Identification depends solely on color
and morphological characteristics
Most common is cotton – however, the
length of the fibers, the twist of the
yarn, and the dye may make a cotton fiber unique
Hemp (pictured) – viewed with polarized light
The fineness or coarseness of the fiber can give the analyst
information about the end-point of the fabric (ie. fine wool is
use in clothing, while coarse wool is used in carpets)
Increasingly replacing
natural fibers in garments
and fabrics
 Man-made fibers can originate from natural fibers but can
also be synthetic
 Polyester and nylon are the most common types of manmade fibers
 Examples
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Acrylic
Nylon
Polyester
Rayon
Spandex
 The
shape of the crosssection of synthetic fibers
may be unique to a
particular manufacturer
and only produced for a
finite amount of time
 Unusual cross-section can
add to the uniqueness of
the fiber and therefore
add to its evidentiary
value
Cross-sectional views of nylon carpet
fibers as seen with a scanning electron
microscope (SEM)
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Fabrics undergo several dying processes to get the desired
color
Fibers may be dyed, and then yarns dyed, and fabrics dyed
Sometimes color is applied to the outside of the fiber like
a “painted” style
How the color is applied, absorbed, and the particular
color are all used as evidence
Any fading or discoloration can have increased evidentiary
value
 Hair
and fiber evidence can be collected
at a crime scene using tweezers, tape, or
a vacuum
 Where the evidence is found can add to
its value
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The fiber should first be analyzed using a microscope for type of
fiber, length, color, diameter, cross-section, damage, crimp (using
stereomicroscope)
Microscopes useful: stereomicroscope, comparison microscope,
and compound light microscope (with polarized light capability)
A side-by-side comparison of the fiber to a known fiber (if and
when it become available) should be done (using a comparison
microscope)
Chromatography can be used to analyze the components of the
color of the fiber (destructive!)
Pyrolysis gas chromatography can be used to determine the type
of an unknown fiber (destructive!)
Infrared Spectroscopy (IR) can be used to determine the type of
fiber (synthetic – organic only)
** finding no fibers does not mean that no contact occured

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