|Material evidence covers
evidence such as glass, fibres
and paint. In general, material evidence refers to anything
that is manufactured
and because so much material evidence exists after a
crime has been committed, it proves to be a powerful
source when attempting to link a suspect or a victim
to the scene of a crime.
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Thinkquest Team 00206
magnification under a microscope can reveal the
colours present in each coat of paint from just
one minute paint sample. Samples of paint which
do show very little are cut and polished to make
the details more visible and then further analysed
using a technique known as microspectrophotometry.
Microspectrophotometry involves electronically
studying the wavelengths of energy that are absorbed
and released by a single paint sample.
Fresh and dried paint samples can be differentiated
to reveal any attempts of hiding old paint layers.
Photo courtesy of www.imageafter.com.
investigators already have a number of suspects,
the paint samples taken from them and the crime
scene can be compared to find a match, which then
incriminates a suspect and strongly suggests that
they were present at the crime scene. Paint flecks
help when a criminal's identity is unknown, as
police databases of the paint work found on vehicles,
houses and buildings can often help trace a hit
and run driver or a break and enter criminal.
Thinkquest Team 00206
Chips of glass are investigated using a number of
different techniques. Using a refractive
index involves investigating the glass's light
bending ability because different types of glass bend
light at different angles. Glass will change its refractive
index when heated and allows for this clue to be measured.
The technique used involves measuring the refraction
when the sample is immersed in heated oil, used as
a agent to prevent the sample from being destroyed
under direct high temperatures. Once heated at the
correct temperature, a laser is then used to measure
the light refraction.
Glass shards can also be valuable evidence when trying
to find an unknown crime scene. Photo courtesy of www.imageafter.com.
When testing the density of a sample of glass, investigators
compare the glass in two different liquids which both
have individual identities. Glass floats in dense,
heavier liquid whereas it sinks in lighter, less-dense
liquid. The investigators combine the liquids until
the glass neither floats nor sinks, but sits halfway
in the liquid formula. The density of the glass is
then worked out using proportions of the two types
of liquid. If no match between a piece of glass found
on a suspect and a sample found at the crime scene
is apparent, investigators consult a database of glass
types which can tell if the glass sample is common,
rare or unusual.
Glass fibres can reveal what object that they were
applied into i.e. the use for which they were manufactured
-a good example is if the glass fibres occur in layers,
they are usually used to strengthen structures made
out of plastic, such as the hull of a boat. Glass
fibres are identified by their point of melting, optical
aspects such as their refractive index, their shape
and appearance underneath a microscope and using chemical
Thinkquest Team 00206
fibres as evidence is very helpful to investigators,
for different types of fibres vary enormously.
There are many different types of fibres and some
of the commonly found ones include animal fur,
plant fibres, synthetic fibres, glass fibres and
leaf material, which can all be identified by
their physical appearance.
Animal fur is significantly
finer than the hair of a human and is different
between certain species. Most forms of animal
hair are covered in scales, which also makes
it very distinguishable from human hair. Synthetic
fibres are also relatively less distinctive
compared to natural fibres when studied underneath
Animal hair is covered in scales and relatively
distinguishable. Photo courtesy of Westchester
County NY Forensics Laboratory.
2004-2005 Thinkquest Team 00206
can recognise leaf material from the shape of the plant
fibre, as particular species of plants contain unique
fibres that identify them. Plant fibres have typical
shapes easily sorted out by botanists, for example,
cotton has twisted fibres that resemble ribbon while
linen looks like tubes that are pointed at each end,
making each easy to distinguish. Such fibres come from
plants, but are also used daily in clothing and may
have the need for analysis.
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