The impact of a good firearms investigator is invaluable to an investigation where a firearm is involved, especially in the case of murder. The ultimate goal of ballistics is to determine if the bullet or casing in question came from a particular firearm.
There can be any amount of evidence in a case that needs to be tested. It could be anything from one bullet fragment to hundreds of casings and ammunition that came from several different firearms. In both cases, the testing done is equally important. The smallest sample can still provide clues to what actually happened.
There are two types of gunshot residue that can be looked at: the type taken from the suspect’s hands, and the type that is collected off the suspect’s clothing. The first type is used to determine if the suspect actually handled or fired the gun or not. If he did not, there will be no residue, and if he did, there will be residue left. The second type is used to determine muzzle-to-target distance, which would tell investigators how far away from the target the shooter was when the trigger was pulled.
Ballistics analysis is performed by trained professionals in labs all over the country. These professionals will look at anything from fired bullets to casings. A microscope is used so no small details are missed or mistaken. Most labs will have a method they use to discharge a weapon, then collect the fired bullet and casings. Usually this is done in a tank of water, but sometimes a box containing cotton waste is used. Investigators can also look at the marks on a bullet collected as evidence and compare them to the grooves inside of a barrel it is suspected the bullet was fired from and determine they match or do not.
In this picture, two cartridge cases are being compared. One was recovered from a crime scene and the other was fired from the weapon in the lab. Note how the marks line up and are similar on both casings.
A proper and thorough examination of bullets, casings, bullet fragments, grooves in the barrel of a gun, or any other number of aspects of ballistics is extremely important to a case under investigation. The results of an examination can prove guilt or innocence, and have the power to change lives and bring closure.
Source: “A Simplified Guide to Firearms Examination.” Forensic Science Simplified. 2013. Web. 25 March 2016.