Baltimore Mayor Brandon Scott is suing the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives for data about where guns used in city crimes originate, the latest move from city leaders to address the proliferation of firearms plaguing Baltimore.

Everytown for Gun Safety, a national nonprofit advocating for gun control, is providing legal assistance for the lawsuit that seeks five years of ATF “trace data,” which shows where a gun police recover was manufactured to where it was sold at retail. That information is regulated by a federal law, known as the Tiahrt Amendment, which only allows it to be shared for law enforcement purposes. Baltimore officials filed a Freedom of Information Act request for the data in September but were rejected.

The lawsuit was filed Monday in the U.S. District Court in Washington, D.C., and seeks to have a judge order the ATF to approve the city’s data request.

Maryland has some of the strictest gun control laws in the nation, including a law against the straw purchase of firearms, which is when someone who can legally buy a gun does so for someone who cannot. Federal law also prohibits straw purchasing, but enforcement at any level is mixed.

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The ATF could produce the data, but the agency does not house it in a readily accessible way and does not have a searchable database of firearms or firearm owners. Instead, according to ATF Baltimore Public Information Officer Amanda Hils, the agency keeps all trace data in nonsearchable formats.

“This ensures ATF is in compliance with federal law that prohibits ATF from maintaining a database while also being able to continue ATF’s mission of addressing violent crime and assisting our law enforcement partners,” Hils said.

Hils declined to comment about the city’s lawsuit; the ATF does not usually comment on pending litigation. The Baltimore Police Department already possesses the data but cannot share it with the mayor or other non-law enforcement officials under the language of the Tiahrt Amendment.

“There is no good reason for this,” acting City Solicitor Ebony Thompson said at a news conference Tuesday. “Keeping the data a secret prevents Baltimore and other cities from educating the public about the sources of illegal guns in their communities. And it benefits no one but the gun industry.”

Named after former U.S. Rep. Todd Tiahrt, R-Kansas, the riders have been attached to Department of Justice appropriations bills for more than two decades and are meant to protect, in part, gun dealers from civil litigation. The riders are backed by the National Rifle Association and other pro-gun groups, and have shielded information that used to be public. A 1995 study, based on what was then publicly available ATF trace data, found that 1% of the nation’s gun dealers were the original sellers of more than half of guns recovered at crime scenes.

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Today, ATF publishes a limited amount of trace data on its website. The most recent annual report for Maryland shows law enforcement around the state recovered 11,137 firearms that the ATF then traced. The most common gun was a 9mm pistol, according to the report.

With the full data, city officials could identify the 10 top sources of guns used in crimes in Baltimore from 2018 to 2022. Law enforcement agencies, including the Baltimore Police Department, already have the power to use the data to conduct criminal investigations, but proving an illegal purchase can be tedious. Gun stores are also mostly out of the Police Department’s jurisdiction; there are none in city limits.

Instead, Scott said, the data could lend itself to other enforcement measures, namely lawsuits against gun stores or retailers who are most commonly linked to crime guns with a high frequency. One of the things the ATF can track is a statistic called “time to crime,” which shows how much time elapsed from the day the gun was purchased to when it was recovered by police in connection to a criminal act. From 2017 to 2021, 1,113 guns recovered in the city were determined to have been sold within a year of police logging them into evidence. That’s 13.8% of the guns recovered that the ATF could determine a time to crime for.

While the majority of Baltimore’s crime guns that can be traced to their point of sale originate out of state, a large portion are bought close to home. About 24% of guns involved in crime in Baltimore recovered from 2017 to 2021 were found within 10 miles of where they were purchased, according to the ATF’s data.

Scott said a more granular view of what stores are supplying the weaponry used in the city could lead to legal action.

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“If we were able to have this information in a hypothetical world, right, and we find out that some gun store in some state is responsible for 30% of the guns that we’ve recovered over the last X amount of years, we’d be foolish to not seek legal action on them because we know that there’s something going on,” Scott said.

Scott’s administration filed a different lawsuit in June 2022, seeking to address the flow of “ghost guns,” or firearms without serial numbers. Ghost guns cannot be traced by the ATF and are making up an increasing number of firearms Baltimore Police recover.

That lawsuit is against Polymer 80, Inc., one of the largest suppliers of 3D printed firearm parts and kits, which are sold online without a background check. Weapons derived from Polymer80 parts make up more than 90% of the ghost guns seized in the city, according to police, and the city is suing them on the grounds that the business has created a “public nuisance” in Baltimore.