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| Material
Evidence |
| 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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Select one of the following topics to read on:
--> Paint
--> Glass
--> Fibres
--> Plant
material
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| Paint |
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Low
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. |
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Fresh and dried paint samples can be differentiated to reveal
any attempts of hiding old paint layers. Photo courtesy of www.imageafter.com. |
| If
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. |
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| Glass |
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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.
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Glass shards can also be valuable evidence when trying to find an
unknown crime scene. Photo courtesy of www.imageafter.com.
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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 analysis.
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| Fibres |
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Analysing
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 a microscope.
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Animal hair is covered in scales and relatively distinguishable.
Photo courtesy of Westchester
County NY Forensics Laboratory. |
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| Plant
Material |
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| Botanists 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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