Ballistic Fingerprints Discovered by Comparison Microscope
Handguns were the firearm of choice in shooting-related crimes, especially in the United States of America. As with most firearms, the fired ammunition components may acquire enough but distinctly unique and reproducible microscopic marks. Such marks aid the identification that such were fired by a single firearm. Making these comparisons is referred to as firearms identification or ballistics.
This forensic discipline requires a microscopic side-by-side comparison of fired bullets or cartridge cases. Viewing one pair at a time, a forensic examiner is able to confirm or possibly eliminate the two items as having been fired from a single firearm. Such tool used by the firearms examiner is called ballistics comparison microscope.
Comparison microscope is important for the forensic ballistics expert in comparing evidence collected such as bullets and spent cartridge casings. The interior of a gun’s barrel is manufactured to have line marks that force the bullet to rotate as it travels along it. These marks and their counterpart, called “lands”, imprint grooves and land impressions on the surface of the bullet. Together with these land and groove impressions, imperfections on the barrel surface are incidentally transferred to the bullet’s surface. Because these imperfections are randomly generated, during manufacture or due to use, they are unique to each barrel. These patterns or imperfections becomes to a signature that each barrel imprints on each of the bullets fired through it. It is this signature on that enables the validation and identification of bullets as having originated from a particular gun. Comparison microscope is used to match the microscopic impressions found on the surface of bullets and casings.
When a firearm, a bullet, and/or a cartridge case are recovered from a crime scene, forensic examiners compare the ballistic fingerprints of the recovered evidences. When the ballistic fingerprint on the test-fired bullet or cartridge case matches the ballistic fingerprint on the recovered bullet or cartridge case, investigators can conclude that the recovered bullet or cartridge case was also fired from the recovered gun. A confirmed link between a specific firearm and a bullet or cartridge case recovered from a crime scene constitutes a valuable lead in the investigation. Such lead may allow the investigators to connect the firearm to a person, who may then become either a suspect or a source of information helpful to the investigation.
