Ballistics
In 1784, someone using a flintlock pistol shot Edward Culshaw. In those days, there were no bullets, as we know them. Gunpowder and a ball of lead were put into the gun's muzzle and packed with paper wadding. A spark made when the gun's hammer struck some flint at the back end of the barrel ignited the powder. When the constable examined Culshaw's wound, he found a piece of newspaper used as wadding to pack the powder in the killer's gun. The prime suspect in the killing was a man named John Toms. When a piece of newspaper found in Toms' pocket was compared with the piece found in the wound, the pieces fit together like two pieces of a jigsaw puzzle. Based on the evidence, Toms was easily convicted. The Toms case was probably the first in America in which ballistics was used to solve a crime.
Much like in Toms case, most investigations start with a crime having been committed. Forensic ballistics and firearm investigation start when there are bullets, cartridges, a weapon, or any combination of the above found at a crime scene. With the evidence, a crime lab can search for clues on these items that could lead to a suspect or possibly prove that the items were used in the crime. By comparing the markings on bullets or cartridges found at the scene with those fired from a suspect's weapon, a ballistics expert can often determine if the rounds came from the same weapon. Just the act of cycling a cartridge through a weapon without firing it can leave permanent scratches in the case that are unique to the weapon.
When a suspect's weapon is examined in the lab, it will be test fired into a box filled with cotton or a tank of water to provide the examiner with the bullets and cartridges with a known history. Using a microscope, the known cartridges are compared with the ones in question. With some patience, skill, and a little luck, experts can definitively say that a certain firearm and no other fired this bullet, or ejected this cartridge.
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