Within about 48 hours of arresting Cleophus Cooksey, Jr. for a double murder on December 17, Phoenix police used ballistic evidence to tie the 35-year-old man to seven additional killings.

The technology that police used to make the connections — a national database of ballistic images that matches guns and shell casings recovered by police — is not new. But experts say it’s a tool that some departments are still using poorly, even as others get great results.  

Phoenix, one of five cities to receive federal funding as part of the Department of Justice’s Crime Gun Intelligence Center initiative, has been working for some time to collect more guns and casings and process them more quickly. Police say quick turnarounds like in Cooksey’s case will help them get more bad guys off the streets — hopefully sometimes even before they hurt anyone.

“What once took weeks can now take place in only a matter of hours,” said Mayor Greg Stanton when announcing that Cooksey was being charged with nine killings, all late last year.

Here’s how the technology works: When a gun fires, it leaves a unique marking on the shell casing it discards. The Bureau of Alcohol, Tobacco, Firearms and Explosives maintains a database of images of these markings called the National Integrated Ballistic Information Network, or NIBIN. Police can enter images of shell casings found at crime scenes into the database. If investigators recover a gun but no expended shell casings, they can test fire it in a lab and create their own. A match in NIBIN can connect a gun to multiple crime scenes or a perpetrator, and possibly solve crimes. 

In the Phoenix case, police said it was NIBIN that made them realize that they were dealing with a serial killer. After police arrested Cooksey on charges that he killed his mother and stepfather, they used NIBIN technology to link him to five other homicides in which they said he used two handguns. They then used other evidence, including cell phone data, surveillance footage, and DNA to bolster their cases and link him to two additional killings.

A number of factors determine whether police departments use NIBIN technology effectively. The first is a requirement that officers collect shell casings every time a shot is fired, even when no one is injured. Experts say a person who shoots and misses one day is likely to shoot and hit someone on another. If police collect and process casings every time shots are fired, it helps them build a wide network of evidence and make matches.  

It also matters how soon police test fire a gun and run casings through NIBIN after they recover them. If police can collect the shell casings, enter them into NIBIN, and make a match quickly, they just might be able to make an arrest soon enough to save a life.

Phoenix Police Sergeant Jonathan Howard said while his department has been using NIBIN for years, officials made some changes late last year that have led to quicker turnaround times. Crime guns and casings used to be taken to an impound warehouse after they were collected, but are now often taken directly to police headquarters for processing. There, they are run through NIBIN machines, usually within hours rather than days.

He said police are now directed to collect all casings, even when no one has been injured.

“Our long-term goal is to process anything that meets the criteria for lawful testing,” he said. “And we are closing that gap quickly.”