Transcript Trace Evidence - Centralia College

Trace Evidence
Part II
Summary
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Microscopic Analysis
Types of Trace Evidence
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Glass
Hair (fur)
Fibers
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Paint
Soil
Gunshot Residue
Hair
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What is hair?
What crimes are hair involved in?
How is hair collected?
How is hair analyzed in the lab?
Trace > Hair
What is hair?
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Natural fibers of animal origin
Terms: human = hair; animal = fur
Usually growing (live root)
Trace > Hair
What is hair?
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Cellular material in the
hair shaft (mtDNA)
Good DNA in the hair
root for forcibly
removed hairs (STR)
Trace > Hair
What crimes are hairs involved in?
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Hairs are shed from people; can link a
person to a crime scene.
Animal fur may also link a person to a
crime scene.
Trace > Hair
How is hair collected?
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Visually by hand or with forceps.
Possibly tape lift.
Packaged in sealed containers.
Trace > Hair
How is hair analyzed?
Look at class characteristics (microscope):
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Color
Medulla, Cortex, Cuticle
Trace > Hair
How is hair analyzed?
Medulla:
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Line down middle of hair
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Species ID or human ID
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Present, absent, or fragmented
Trace > Hair
How is hair analyzed?
Cortex:
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Color of hair
Species ID or human ID
May contain pigment blotches
May contain air pockets
Trace > Hair
How is hair analyzed?
Cortex:
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Humans = 1 color entire length
Animals = color can vary at
root/middle/tip
Trace > Hair
How is hair analyzed?
Cuticle:
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“Scales” on outside of hair
Species ID only
Humans = imbricate
Trace > Hair
How is hair analyzed? (cuticle)
Procedure:
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Put clear nail polish on slide.
Place hair in nail polish; wait
to harden.
Remove hair; look at
indentations in nail polish
(microscope).
Fibers
Fibers are very useful as trace evidence:
 Vary widely in class characteristics
color, shape, chemical composition, etc.
 Easily transferred from one source to
another (carpets, clothes, etc.)
 Significant persistence (won’t degrade)
Trace > Fibers
How are fibers used as evidence?
As with other trace
evidence, fibers can be
transferred to/from a
person or objects linking
them to one another.
Trace > Fibers
How long do fibers persist?
Most fiber evidence is lost (fall off) a short
time after the transfer occurs.
The fibers that do remain will be persistent.
Trace > Fibers
Fibers can be classified into three
main categories:
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Natural (animal, plant, mineral)
Manufactured
Synthetic
Trace > Fibers > Natural
Natural Fibers:
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Found in nature
Can be artificially colored or treated
Cotton
Wool
Hemp
Trace > Fibers > Natural
Animal Fibers
Wool - Hairs from sheep
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Most common of animal fibers
 Hairs are spun to form thread
Silk - comes from silkworm
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Spun as double filament (separated before use)
 Because of length, doesn’t shed easily
Other Hairs from Animals
Trace > Fibers > Natural
Plant Fibers
Cotton - seed hairs of cotton plant
by far most common fiber (find almost everywhere)
Under microscope,
fibers resemble
twisted ribbon
Trace > Fibers > Natural
Other Plant Fibers:
Linen - stem fiber from flax plant
Kapok - from seed hairs of kapok plant
Other fibers - Manila, hemp, sisal, jute
Trace > Fibers > Natural
Mineral Fibers
Asbestos - crystalline material

Used to be used for insulation
 Fractures into thin rods that
can get into your lungs; can
kill you
 Not used much anymore
Trace > Fibers
Filament vs. Staple
Filament: Long continuous fiber (like silk)
Staple: Filament is cut into smaller pieces;
staples are spun together to form thread
(like cotton)
Trace > Fibers > Manufactured
Manufactured Fibers
Regenerated Fibers
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Cellulose is dissolved,
then resolidified to form
the polymer fiber
Can occur in filament or
staple form
Example: Rayon
Trace > Fibers > Synthetic
Synthetic Fibers
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Man made
Can also be filament
or staple
Examples:
Nylon and Polyester
Trace > Fibers > Synthetic
Synthetic Fibers
Acrylics
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More common as
evidence
Usually in staple form
Staples spun together,
similar to wool
Trace > Fibers > Analysis
Begin by identifying and comparing class
characteristics for unknown sample
(evidence) and known sample.
Unknown
Known
Trace > Fibers > Analysis
Fibers from rug in a van.
Fibers found on victim.
Trace > Fibers > Analysis
Class characteristics
Color: microscopic examination
Size: length and width can be measured
Shape: cross section is viewed
Trace > Fibers > Analysis
Class characteristics
Refractive Index – n. The ratio of the speed of light in air
or in a vacuum to the speed of light in another medium.
Other microscopic properties (PLM)
Trace > Fibers > Analysis
Class characteristics
Chemical Composition: determined by
advanced instrumentation
Trace > Fibers > Cordage
Threads, Yarn, Rope, Cordage
Smallest component is fibers (staple) twisted
together to form thread or is a filament.
This thread can then be twisted with other
threads to form a thicker thread (string, etc.)
This thicker cord can then be twisted with
other thicker cords, etc.
Trace > Fibers > Cordage
Threads, Yarn, Rope, Cordage
Small cords or fibers twisted together to
form larger cords
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At each step, the
number of cords
can be counted.
At each step, the
twist direction is
either “S” or “Z”
Fiber
niso
nll
n
Biref
MP (ºC)
K1
1.518 to 1.528
1.544 to 1.551
1.505 to 1.516
0.035 to 0.039
Does not melt
K2
1.777 to 1.877
2.050 to 2.350
1.641 to 1.646
0.200 to 0.710
Does not melt
K3
1.512 to 1.521
1.510 to 1.520
1.512 to 1.525
-0.001 to
-0.005
Does not melt
K4
1.538 to 1.539
1.530 to 1.539
1.538 to 1.539
-0.000 to
-0.002
192 – 210
K5
1.533 to 1.545
1.568 to 1.583
1.515 to 1.526
0.049 to 0.061
210 – 230
K6
1.540 to 1.541
1.577 to 1.582
1.515 to 1.526
0.056 to 0.063
250 – 264
K7
1.522
1.553
1.507
0.046
182 – 186
K8
1.535 to 1.539
1.568 to 1.574
1.518 to 1.522
0.050 to 0.052
133 – 138
K9
1.567 to 1.575
1.632 to 1.642
1.534 to 1.542
0.098 to 0.102
282 – 290
K10
1.474 to 1.478
1.474 to 1.479
1.473 to 1.477
0.002 to 0.005
245 – 260
Q
1.520
1.515
1.513
-0.003
Does not melt
Glass
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What is glass?
What crimes are glass involved in?
How is glass collected?
How is glass analyzed in the lab?
Trace > Glass
What is glass?
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Made from fused inorganic materials
Amorphus; not crystalline (molecules not arranged)
Varies in elemental formula
Many shapes and colors
Trace > Glass
How is glass involved in crime?
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Small fragments can be used as trace
evidence (link objects/people)
Crime scene reconstruction
Trace > Glass
How is glass collected?
For reconstruction, detailed photographs
can be taken or the entire pane of glass is
collected.
Trace > Glass
How is glass collected?
For trace evidence, usually visually
collected with forceps and packaged in
plastic bags.
Trace > Glass
For reconstruction:
Radial cracks
Concentric cracks
Trace > Glass
For reconstruction:
Concentric cracks
Radial cracks
Concentric cracks
Trace > Glass
For reconstruction:
1.
Determine the direction of projectile.
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When looking at a radial
section, conchoidal
fractures point back to
the origin of the break
Core usually on opposite
side of the origin
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Trace > Glass
For reconstruction:
2.
Determine the order of projectiles when
dealing with more than one.
2
1
3
Trace > Glass
For reconstruction:
2.
Determine the order of projectiles when
dealing with more than one.
2
1
3
Trace > Glass
For trace analysis:
Associate unknown glass found at the crime
scene with known samples to determine
the source.
Done with microscopic analysis
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Color, curve, thickness, etc.
Refractive index: Determined by placing glass
in oils of different refractive indexes
Trace > Glass
Refractive index:
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Low relief = no outside line
R.I. of glass and oil are similar
High relief = thick outside line (Becke line)
R.I. of glass and oil are different
Paint
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What is paint?
What crimes are paint involved in?
How is paint collected?
How is paint analyzed in the lab?
Trace > Paint
What is paint?
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Colored chemical coating
Covers cars and houses
Trace > Paint
What is paint?
Paint contains 3 things:
 Vehicle – binds components together
 Pigment – gives paint color
 Extenders – used to modify gloss, texture,
opacity, etc.
Trace > Paint
What crimes are paint involved in?
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Hit and Runs – paint from car left at scene
Other vehicular accidents
Home invasion – windows; on suspect
Trace > Paint
How is paint collected?
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Visually by hand or with forceps.
Packaged in sealed containers.
Trace > Paint
How is paint analyzed?
1.
2.
Possibly a physical match (jigsaw-like)
Associate the unknown paint with a
known sample (class characteristics)
Trace > Paint > Analysis
How is paint analyzed?
Chemical composition determined by FT-IR
Chemical “Fingerprint”
Trace > Paint > Analysis
Paint can be in multiple layers
Each layer is analyzed to determine its
physical and chemical properties.
Soil
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What is soil?
What crimes involve soil?
How is soil collected?
How is soil analyzed in the lab?
Trace > Soil
What is soil?
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Mixture of animal and vegetable materials,
and minerals
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In many ways, soil has a unique
composition in a given area.
Trace > Soil
What crimes involve soil?
Due to the widespread location of soil
(earth), it can be used to associate people,
objects, and scenes in numerous cases.
Trace > Soil
How is soil collected & analyzed?
Collected in jars or vials.
Materials in soil are identified and quantified.
Analysis relies on soil composition being:
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Consistent over time in one location
Different in different locations
Gun Shot Residue (GSR)
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What is gun shot residue (GSR)?
What crimes are GSR involved in?
How is GSR collected?
How is GSR analyzed in the lab?
Trace > Gun Shot Residue
What is GSR?
Mixture of materials that originate from the
firing of a gun.
From the
barrel
From the
chamber
Trace > Gun Shot Residue
What is GSR?
GSR will fall onto hands of person firing
the gun.
Trace > Gun Shot Residue
What crime is GSR involved in?
Crimes with guns
Trace > Gun Shot Residue
How is GSR collected & analyzed?
Hand/glove/paw is swabbed
Analysis:
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Elements barium and antimony are found in
high levels.
Use powerful microscopy (SEM)
Use chemical tests (color change reactions)