Every time a handgun is fired, it creates evidence. Watch how police use that evidence to connect criminals to their crimes. Unfired bullets are referred to as cartridges. A cartridge has five main components: When the trigger of the gun is pulled, the hammer hits the firing pin. The firing pin strikes the cartridge shell at the location of the primer.Watch it happen... Next, the impact ignites the primer, which ignites the gunpowder. The explosion causes the the bullet to leave the shell and fly down the barrel. A spinning bullet flies in a straighter path, due to gyroscopic force. The bullet is caused to spin by grooves inside the gun barrel. These grooves are called rifling. Even fresh from the factory, the rifling of every gun barrel has microscopic differences. These differences leave unique marks on each bullet as it leaves the gun. The Integrated Ballistics Identification System (IBIS) begins by scanning the bullet for these grooves. All the marks around the exterior are captured as one digital file. This file can be manipulated to show every side of the bullet at once.The depth of the grooves can also be enhanced to bring out detail. Bullets from separate crime scenes can be compared to match these grooves.When a gun becomes evidence, it can be test-fired in a lab to provide a reference bullet, linking the gun to all the previous shootings that police have catalogued. But the bullet is only one piece of evidence that the gun produces. When the shell of the cartridge leaves the firing chamber, it also bears unique marks from the firing pin, the ejector, and the breech face.Shells are often left behind at crime scenes.Every time the Toronto Police find one, it is entered into the IBIS system. Just like spent bullets, spent shells can be analyzed for microscopic matches.Over time, this evidence creates a profile of a gun in the community, even if the gun is shared by more than one person. October 24, 2005: A man driving a borrowed car is ambushed in a Toronto laneway.The driver is shot several times in the chest, but survives. October 25, 2008: Gunfire outside the Duke of York Tavern wounds four and kills Bailey Zaveda. A suspect, Robert Weese, turns himself in. But with no murder weapon and no confession, the outcome of the case is uncertain. December 10, 2008: Two young men in a car are accosted by three others.The three force their way into the back seat of the car, rob the two at gunpoint and flee. Toronto Police search the residences of all three suspects.Two firearms matching the description of those used in the robbery are seized. Evidence from each of the three crimes is submitted to the Centre of Forensic Sciences (CFS) for examination. Using IBIS, firearms technologists process the ballistics data through the Canadian Integrated Ballistics Identification Network (CIBIN). Analysis shows that one of the firearms seized, a 9mm pistol, was also used during the laneway ambush and the Duke of York homicide.", Accused of using that pistol, Weese is found guilty of second-degree murder and four counts of aggravated assault.He is sentenced to life in prison with no chance of parole for 22 years. For the latest on Canadian forensics technology, read our stories below.