Page 12 - Shot In The Dark Bullet Striations

firearm works. In a semiautomatic firearm (i.e. a a gun can also be easily altered with a nail or metal
gun that does not require the user to manually cock file or by shooting the bullets after putting dirt,
the gun’s hammer or set a bullet before every shot powder, or even toothpaste on the bullets or in the
fired), the bullet is fired by pulling the trigger which gun barrel. This makes the investigator’s job much
releases a spring that rams the firing pin into the more difficult, or even impossible.
end of the cartridge. This causes the primer to ignite
the gunpowder that supplies the energy to project By the year 1500, barrel rifling had been introduced
the bullet from the barrel of the gun. As the bullet by the German Emperor Maximilian. This new way
travels down the barrel it is squeezed through spiral of making gun barrels was thought to improve
grooves, called barrel rifling, which cut into the side accuracy and precision. The lands and grooves left
of the bullet and impart a spin upon the projectile. on bullets after firing them, however, was not used
This stabilizes the bullet as it exits the muzzle of the to link a gun and bullet together until much later, as
weapon, improving accuracy in the same manner it was not until the end of the 1800’s that this idea
in which a quarterback’s spiral pass improves the was introduced as a form of firearms identification.
accuracy of a football. The markings made by the Alexandre Lacassange (1844-1921) of France was
rifling on the bullet are called striations, or striae. The one of the first to attempt to identify and match an
grooves (or scratches) and lands (or raised surfaces) individual bullet to a gun barrel. A physician working
are the portion of the bullet examined by the in the forensic medicine division of the University
computer programs and experienced professionals of Lyon, Lecassange wrote an article outlining his
to link crime scene bullets to the gun that fired them. findings which served to pave the way for further
Only bullets used from handguns and rifles can be development of the science of ballistic imaging.
used for ballistic imaging because shotguns fire a
cartridge that contains tiny pellets or a metalslug and As this new concept began to enter into the field
possess a smooth, un-rifled barrel that does produce of forensic analysis, a more sophisticated and
consistent markings. The cartridges from a fired precise technology was developed to compare
bullet will also have identifying marks on its surface. questioned bullets and the standards fired by
With semiautomatic firearms, the cartridge is the gun in question. Calvin Goddard, one of the
automatically ejected from the gun and is usually left men that developed this technology, designed
at the scene unless the criminal has equipped their a microscope to closely compare marks left on
firearm with a spent cartridge catcher. Cartridges are multiple bullets to one another. At that time,
often not present at the crime scene if a revolver is the design of typical microscopes enabled an
used, however, as the used cartridges are manually examiner to look at just one bullet at a time, making
removed from the gun during reloading. bullet comparison difficult. The examiner had to
remember the pattern of marks on one bullet and
These markings have the potential to be then separately view the other bullet. In 1925, the
consistently made over and over again on each comparison microscope was invented, comprised
bullet that is fired, with each individual gun leaving of two microscopes connected by an optical bridge.
a similar pattern. Many people refer to this as This design allowed separate objects to be viewed
ballistic fingerprinting. The word “fingerprinting” simultaneously in a split-view window. The viewer
implies that the mark is unique and unchangeable could then immediately note findings between
from each bullet fired. The truth, rather, is that the two items without having to use two separate
these markings change over the lifetime of a gun as microscopes or having to switch back and forth
the barrel rifling is worn down by bullets traveling between the two items. When using a comparison
through the chamber and by cleaning. The barrel of microscope today to compare striae, the

12 THE MYSTERY OF LYLE AND LOUISE