COLUMBUS, Ohio (WCMH)–When gunshots are fired during a crime, investigators work to find out who pulled the trigger, and from where the gun originated.

Firearm tracing can be a critical crime-fighting tool because learning how guns get into the wrong hands is one way to prevent future crimes.

Agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives’ Columbus office said firearm tracing proved to be incredibly useful in 2018 after two Westerville police officers were killed.

That February, Officers Eric Joering and Anthony Morelli responded to a 911 hang-up call involving domestic abuse when they were shot to death.

Quentin Smith was quickly arrested and charged with both murders, for which he is now serving two life prison sentences without the possibility of parole.

A convicted felon at the time of the shooting, Smith was not legally allowed to possess the gun he used to kill the officers.

“Getting the possessor is one thing, but getting the individual putting the firearm in the hands of those users is just as critically important,” said the ATF agent who investigated how Smith got the gun.

The agent spoke with NBC4 Investigates under the condition that her name and face were not be shown in order to protect her safety and the safety of other undercover ATF agents.

Investigators recovered the gun at the scene of the Westerville shooting, which allowed them to immediately send the gun’s serial number and other identifying information to the ATF’s National Services Center in Martinsburg, WV, where every firearm trace in the United States is conducted.

Federal law requires licensed firearm dealers to keep records of who buys each gun — whether it’s a private citizen or another dealer. A firearm trace begins at the gun’s manufacturer and following that trail of records by calling each licensed dealer until the first unlicensed purchaser is identified.

Traces can sometimes take up to two weeks, but in this case, Columbus investigators asked for an urgent trace. An urgent trace can return results in hours, or even minutes.

The trace on the gun used to shoot Joering and Morelli revealed a critical piece of information: a name.

“That shooter had received his firearm through what we would define as a straw purchaser,” the agent said. “So someone went on behalf of the shooter to acquire a firearm for him because he could not legally pass a background check.”

That straw purchaser was Gerald Lawson III, who is now serving a five-year sentence in federal prison as a result of the investigation.

“We also were able to document through social media the connection – or the relationship between the purchaser and the possessor,” the agent said, adding that the connection was also backed up by executed search warrants and interviews with witnesses.

As the nation, and Columbus, endures an increase in gun crime, the agent said firearm traces are an even more crucial piece of the puzzle.

“I am focusing on how those guns are getting diverted to the criminal market, (and) I think there is an increase of individuals obtaining firearms on behalf of other people,” she said.

It is important to point out that researchers said it’s almost impossible to determine the proportion of gun crimes committed by an illegal possessor, versus someone who had the gun legally.

That’s because gun laws differ by state, and many gun crimes remain unsolved.

Some researchers on the university level have done local and regional studies on this by surveying inmates, like this one from Johns Hopkins University. In many of those studies, a significant number of those inmates said they got their guns illegally, although the number tends to vary.