Essay On Firearms And Tool Marks

In the CSI: Web Adventures Flash game, I began by going through my Firearms and Tool Marks training. The introduction relayed that I was going to figure out how to match a bullet to the gun that fired it using forensic techniques. The training showed me the various components of a gun – these included the different phases of a gun being fired, including the firing pin hitting the cartridge, the slide pulling back to eject the cartridge, and a new bullet sliding into place. The most important part of this section was learning about rifling – the spiraled marks that help spin the bullet out of the barrel.
Next, I learned about the bullet itself – how caliber is indicative of the diameter of the bullet, and the projectile shoots out from the cartridge case once the firing pin is struck. After that, I was shown the characteristics of a bullet. The rifling impression varies between conventional or polygonal, the difference being the smoothness or visibility of the grooves. I learned that the number of grooves found on a bullet determines its rifling number, and it can differentiate between left or right twist, as it comes out of the barrel in a certain direction.
I also determined the difference between class and individual characteristics of a gun – class characteristics are indicative of the type of gun it is (rifling, serial number, caliber), and individual characteristics pertain to how the specific gun fires (striations, etc.). I was then sent to the firing range, where I had to shoot the correct answer to the questions about the parts of a gun/cartridge, or components of a fired bullet.
After the training, I was tasked to work on a case. There was a four-person gang shooting in which an innocent bystander was killed. It was left up to me to figure out which of the four handguns (A Smith & Wesson, a Kahr and two Tauruses) was the murder weapon. A bullet was taken from the victim for analysis, so that I could search for class and individual characteristics. Given the diameter of the bullet, I determined its caliber as 9 millimeter. Since the striations on the bullet were deep and easily visible, I noticed that the gun used conventional rifling. That took the Kahr out of consideration since it uses polygonal rifling. The rifling number of the bullet was determined to be 6, as there were 6 grooves in the bullet. That eliminated the Smith and Wesson, leaving only the two Tauruses as the possible options.
From there, we had to decide which of the two Tauruses was used through comparing their individual characteristics. A watertank was used to fire bullets from each of the guns in order to compare them to the bullet at the crime scene. Using a comparison microscope, I then looked at the two different bullets, focusing them up on the comparison microscope and seeing which one matched the striations. After checking all the angles on Suspect A’s bullet, I saw that it was not a match. Looking at Suspect B’s bullet, however, showed a matching set of bullet grooves on each bullet.