TUCSON (KVOA) - It is a tool police have used for over two decades.
Over time the technology has improved immensely.
Technology that compares ballistic evidence to help solve and prevent violent crimes involving firearms.
It's called National Integrated Ballistic Information Network.
A shell casing was collected at a crime scene. It does not look like much but to the trained eye of an expert it says a lot.
Erin Anderson is the Gun Crimes Intelligence Coordinator at the Tucson Police Department.
She sometimes processes up to 50 shell casings a week.
"Every firearm has a sort of unique fingerprint," she said.
On this day she was analyzing a casing Tucson Police recovered from a bus stop near 36th and Kramer.
A woman waiting for the bus called police and said, she had been approached by a man.
"A male attempted to start a conversation with her, and also attempted to solicit sex from her," Sgt. David Contreras said.
The woman refused, the man then took out a firearm and fired the gun up into the air. That's when she called police.
That casing was recovered is getting ready to go into the NIBIN system.
"That machine is going to advise us if that cartridge has matched any previous cartridges that we've collected at crime scenes," Sgt. Contreras said
Anderson said, she will go through and take a series of pictures and Nibin technology compares the pictures.
As Anderson looked at the imaging she said she liked what she was seeing.
"There's lots of potentially unique information here," Anderson said.
Unique because of 3-D technology added to NIBIN.
"We had some incredible work that we did in 2016 with some repeated shootings some firearms that traditionally I think back before we had the 3-D resolution that would have been very hard for the system to pick up," Anderson said.
Once pictures are ready, they're submitted to the NIBIN database where technicians conduct a digital review of the results.
"Now that we have this specific cartridge if it will be involved in any future crimes that maybe committed by the same perpetrator or by anyone firing that same firearm," Contreras said.
The shell casing alone is not enough for a probable cause to make an arrest. It's just a very important piece of the investigative puzzle.
According to ATF, who established NIBIN in 1997, 223,000 and more than 126,000 hits have been identified during its 23-year-history.