Behind the Scenes: State Crime Lab shows how experts trace bullets back to their guns

SEATTLE -- Every shell casing found at a crime scene can be a crucial piece of evidence for detectives working to match a bullet to a gun. Caleb Conn works at the Washington State Crime Lab in Seattle and says, “This is what an unfired cartridge would look like. When you fire it, the bullet will go out, go downrange, whatever you’re aiming at. What’s left is the fired cartridge case. A lot of people refer to this as the brass or the shell casings.” And every shell is different. Each firearm leaves its own unique mark every time it’s fired, much like D-N-A. Because of that unique mark, it’s able to be traced with a high level of certainty. “What we’re looking really looking at is all these microscopic striated lines across this across the base of  the primer that are unique to each gun, and are reproducible every time you fire that gun, said Conn. And because NIBIN or Integrated Ballistic Information Network can use those individual markings on fired cartridges, it’s also the most powerful weapon to link gun crimes. Terry McAdams is a lab manager at the crime lab and explains the system’s ability to connect shootings saying, “So if you get a  call in the middle of the night, ‘hey someone is shooting a gun.’ You drive along, the police turn up and pick up the cartridge cases, give  them to us, and low and behold that might hit on a homicide.” NIBIN was developed in the mid-90s by the A.T.F., but has undergone several upgrades, including the 3-D high resolution version that’s in operation today. It takes about seven minutes to upload each cartridge which is weeks, even months faster than the previous method. Conn recalls, “This is a tool where you used to have all the unsolved shootings in the area would go into a card file and it was on the firearms examiners when they were on a new case to remember, I remember something like this that had a unique mark on it , they’d go back through the card file and try to compare it manually.” A firearms examiner still has to take a look at the computer matches and confirm the hits, but it’s the best way to trace bullets back to their firearms in minutes and keep detectives on target to get their bad guys. McAdams adds, “It’s a highly effective tool just like fingerprints are not an end all, or DNA is an end all, you still have to do the police work  to go with it, but it gives you that information which is vital.” The crime lab uploads about three hundred casings a month. They have had over 600 “hits” since the system’s invention. Some law enforcement agencies are unaware that this tool exists and is free to them. The hope is that NIBIN will be used more often to link and match more shootings in the future.