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| Artillery |
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| The research
done by forensic scientists with regards to artillery is very important,
particularly in countries where guns are easily obtainable. Despite
what criminals think, plainly removing the gun from a crime scene
does not prevent the possibility of leaving incriminating evidence
at the scene. |
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Choose one of the topics below to read more:
--> The evidence
--> The gun
--> The bullets
--> Gunshot residue
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| As a criminal
fires a gun, the evidence is thrown in every direction. The first
piece of evidence dispersed from a gun during shooting is the most
deadly of all, the bullet. The second piece of evidence is the used
cartridge
case that contained the bullet inside the gun. The third is
the burnt gunpowder expelled from the bullet and barrel of the gun
during the firing. Then lastly, the noise the gun makes as it fires
its potentially fatal bullet, for those other than the victim can
hear it. In order to understand how each of the pieces of evidence
expelled from a gun can help forensic scientists, it's important to
understand how a gun works. |
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| The
Gun |
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| Most guns work in a similar way, that
is, when the trigger is pulled, it makes the firing
pin hit the back of the sealed unit (bullet) and in turn, ignites
the small pressure-receptive charge
called a 'primer'. The primer then sets off an explosive powder in
the bullet (or in the case of a shotgun, pellets), forcing it to move
down the barrel, where it is expelled towards the target. The power
of the explosion, a powerful chemical reaction, will give the bullet
speed and force. Simple guns need to be reloaded after one or two
shots, though most guns have a bullet holding area that can usually
store up to five bullets or more. Semi-automatic weapons have an explosion
that pushes the bullet out, as well as ejecting the used bullet cases.
The weapon then automatically reloads a new bullet and pulls back
the firing pin, in preparation for the next shot. In the case of automatic
weapons, when the trigger is held back, the gun will continue firing
until the bullet holding area is empty. The most common firearms come
in the form of a revolver, a semi-automatic revolver, machine guns,
hunting rifles and shotguns (loaded with pellets). |
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| The
Bullets |
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In
the case of a shooting, investigators must find out how many
shots were fired, where the bullets went and how each bullet
got to where it is. This is done by talking to witnesses who
heard the shots or saw them being fired and also looking for
the used cartridges that may have been left on the ground. If
the shooter dropped the weapon, it is possible to tell how many
shots were fired by counting how many shots remain in the bullet
holding area. Once it has been established exactly how many
bullets were fired, the next step is to find all the bullets.
An x-ray
of the victim will show bullets lodged in the body as dark shadows.
Bullets lodged in materials that are soft are especially helpful
in an investigation, as the marks left behind can be useful
in the identification of the weapon that fires it. If bullets
are dented beyond analysis upon contact with a hard surface,
it is still important to find the bullet's point of impact,
as it enables investigators to trace the path from the barrel
of the gun to its final resting place. This is done using lengths
of rod and pieces of string, as well as lasers,
but lasers can only be sighted and photographed in specific
light conditions. |
| *The
daily work of the firearms department. Photo courtesy of Californian
Association of Criminalists. |
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Gunshot residue
is found in a circular shape around the victim's bullet wound and
most importantly, on the suspect's hands and clothing. Residue that
is found on a suspect's hand can provide proof that the suspect handled
and fired a weapon recently, but the absence of residue is not enough
to prove innocence. Washing the hands can remove all traces of gunshot
residue and some weapons do not expel any residue at all. Because
of this, investigators will often take swabs of a suspect's clothes
and face to try and find traces of residue. Other traces of residue
may not be just from the bullet, but also from the oil and metal that
can come in contact with the hands whilst loading a gun. |
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Scientists use these ballistics tanks to study the projection of different
bullets. Photo courtesy of www.greenvillecounty.org. |
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