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.
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.
*Ammunition,
the fuel behind a gun's deadly shot. Photo courtesy
of www.imageafter.com.
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).
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.
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.
*
Scientists use these ballistics tanks to study the projection
of different bullets. Photo courtesy of www.greenvillecounty.org.
