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Every year, thousands of guns once owned by police departments are used in crimes across the U.S. Many start out as the pistol in a cop’s holster, but are later sold through an opaque network of gun dealers, recirculated into the public market and eventually recovered by other law enforcement officers.

The federal government knows which departments’ guns end up in crime scenes most often. They know which gun stores resell the most former police weapons that are later used in crimes. They know the journeys those guns travel, the crimes they’re committed with, and in many cases who committed them. 

But Congress won’t let them tell the public what they know. 

In 2003, Republican Member of Congress Todd Tiahrt of Kansas introduced an amendment to a federal spending bill that severely restricted the ability of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) to release details on specific guns they trace. 

As the only agency with access to gun transaction data, the ATF traces hundreds of thousands of firearms a year on behalf of every law enforcement agency, from small town sheriffs to the FBI.

Between 2017 and 2021, the ATF traced more than 1.9 million guns, according to a March 2024 report. But under the Tiahrt Amendment, they can only release the most basic aggregate information about them: totals by year, by state, by type of gun. It’s rare to obtain more detailed data.

In 2017, Alain Stephens, an investigative reporter at The Trace — CBS News’ partner for this investigation — filed a Freedom of Information Act request with the ATF for the number of guns traced back to law enforcement. The information existed in the ATF’s database, but they didn’t release it.

The investigative journalism outlet Reveal from the Center for Investigative Reporting sued the ATF on Stephens’ behalf. After three years of litigation, the ATF finally produced a single spreadsheet. The data had two columns: the year and the number of guns it had traced to domestic law enforcement agencies. The numbers included guns that were lost or stolen, but also documented weapons that were sold by law enforcement.

It confirmed what had previously been widely reported before Tiahrt made it nearly impossible to get this information: police sell guns, and those guns often end up in crimes. 

In 2022, The Trace and CBS News began working to answer a key question: which departments sell their guns, and was it possible to trace those guns to crime scenes ourselves? 

Journalists at CBS News and The Trace filed more than 200 public records requests, asking local departments for records of their gun sales. We focused mostly on the nation’s largest departments. We also contacted some smaller agencies near CBS News’ local stations in major U.S. cities. 

Through those requests and dozens of interviews with police officials, we compiled a list of more than 140 departments that sold their guns. That’s about 9 out of 10 of the agencies that responded to our requests — though many agencies refused to answer or heavily redacted the records they did provide. 

We also submitted requests for data about guns recovered by police departments at crime scenes. Using that data, data gathered by The Trace for a previous project on lost and stolen guns, and tens of thousands of pages of federal court filings, we built a database of nearly 1 million guns used in crimes. 

Under federal law, every gun in the U.S. must have a serial number — an identifier unique to the weapon’s manufacturer that the ATF can use to trace it. 

We compiled a list of serial numbers of about 30,000 guns sold or traded by police — a small fraction of the guns police sold. By searching that small sample of serial numbers against the records of 1 million guns recovered by police, we identified dozens of potential cases where sold police guns were used in crimes. 

We then fact-checked each case, reviewing records and interviewing police officials to find out what happened.