Most people naturally lose up to 100 head hairs per day.
Because of this, there is ample opportunity for transfer of
this material on to another person or surface at a crime
scene. Examination of microscopic characteristics using a
comparison microscope can associate a person to an unknown
hair recovered from a scene or another person.
Fibers and Fabric
Fibers may be transferred in a variety of
ways. Carpet fibers may be transferred to shoes as an
individual walks across it or fibers from clothing may be
transferred onto a vehicle when it strikes a pedestrian.
Fibers may be compared using a comparison microscope.
Additionally fiber types may be identified using a PLM and a
FTIR. Fabrics may be examined to determine if damage present
was caused by cutting, tearing or normal wear.
Paint can be transferred in many
different ways. Paint can be transferred from one vehicle to
another during a hit and run or onto a tool used to pry open
a window. Instrumental analysis by microscopy, FTIR and SEM/EDS
can determine the type of paint and conduct comparisons
between known and unknown sources.
Impressions can be made by footwear,
tires, fabric, and tools. Unknown impressions can be
examined to determine relevant manufacturer information, and
comparisons to known sources can be conducted. If enough
unique characteristics are present in an unknown impression,
it can be identified to a specific source.
Gunshot Residue (GSR)
Items are examined for the presence of
gunshot residue produced from the primer of a cartridge
casing as a gun is fired. Examiners use the SEM/EDS to
detect microscopic particles consistent in morphology and
elemental composition with GSR particles.
When an object is broken, torn, or cut,
unique edges may be formed. By examining those edges
macroscopically and microscopically, the edges may be fit
together like puzzle pieces. If the edges can be fit
together, it can be said that they were at one time a single
object. Car parts, tape, fabric, and glass are just a few of
the many types of evidence where a physical match can be
When a suspicious fire occurs, specially
trained investigators will examine the scene. If they
suspect that an accelerant may have been used, evidence is
collected and brought to the lab. A GC/MS is used to
determine the presence or absence of petroleum products and
non-petroleum based accelerants.
When a piece of
evidence is brought to the laboratory and no other units are
able to analyze it, the Trace Evidence Section will often
receive the evidence and attempt to identify it through the
use of numerous microscopic and chemical analyses and
compare it to a known source, if available.
Potentially, every piece of instrumentation in the section
may be used to analyze the material. Examples of this type
of evidence include: pepper sprays or maces, acid/foil
bottle bombs, exploding bank dye packs, general unknowns,
lamp filaments and pressure sensitive tapes.