BALTIMORE (AP) — Glock pistols are a popular choice for people committing gun crimes, in part because they can be easily converted into fully automatic weapons using a small device, according to a new report based on data from nearly three dozen U.S. cities.

Often called Glock switches or auto sears, the devices have received heightened attention in recent years because they’re increasingly turning up at crime scenes. They effectively turn semiautomatic weapons, which fire one bullet per trigger pull, into machine guns that can spray continuous gunfire.

Authorities believe the shooters who killed four people and injured 17 others in Birmingham, Alabama, last weekend were using conversion devices to make their guns more powerful. About 100 shell casings were recovered from the scene.

A report by the anti-violence organization Everytown for Gun Safety says criminals often choose Glocks because they’re relatively cheap and easy to operate and modify. But the brand is perhaps best known for its popularity among law enforcement officers, who almost exclusively carry Glock handguns.

The report was released this week ahead of a conference Thursday in Baltimore hosted by Mayors Against Illegal Guns, a group that falls under Everytown’s umbrella. The organization called on Glock and other weapons manufacturers to take responsibility for their products and do more to prevent violence.

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“We have to build that level of accountability for them as well,” Baltimore Mayor Brandon Scott said in an interview. “At some point, as a country, the sanctity of the lives of Americans has to begin to outweigh the sanctity of American guns.”

A spokesperson for Glock didn’t respond to an email seeking comment.

Scott and other mayors said while local elected officials are often at the forefront of pushing for better gun policies, Congress must also step up and address the issue.

Researchers found that four gun manufacturers accounted for over 40% of the recovered guns they studied, with Glock alone accounting for 18%. The team compiled data from 34 U.S. cities about guns recovered from crime scenes in 2023.

“They’re basically profiting off of pain,” said John Feinblatt, president of Everytown. “They’re prioritizing profits over safety.”

Meanwhile, the prevalence of machine gun conversion devices has increased dramatically — 570% between 2017 and 2021, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives. The devices are banned under federal law. Most are small pieces of metal or plastic made with a 3D printer or ordered online.

The report also found that recoveries of Polymer80 ghost guns — untraceable, unassembled firearms that can be purchased online — increased nearly 1,200% across 28 cities over the past five years. Those numbers have started trending downward following the implementation of a new federal rule and a wave of state legislation banning the weapons, according to the report. Polymer80, once a leading manufacturer of ghost guns in the U.S., also shut down operations last month after a deluge of lawsuits.

The city of Baltimore was among those who filed suit. City officials announced a settlement agreement in February after the Nevada-based company agreed to stop selling its products to Maryland residents.

The city’s lawsuit accused Polymer80 of intentionally undermining federal and state firearms laws by designing, manufacturing and providing gun assembly kits without serial numbers to buyers who don’t undergo background checks. It was filed the same day Maryland’s statewide ban on ghost guns went into effect in 2022 following a law change that expanded the definition of a firearm to include “an unfinished frame or receiver.”

A year later, recoveries of ghost guns in Baltimore had dropped 25%, according to the report.

Gun violence has also decreased significantly in the city over roughly the past two years, a positive trend that experts and officials attribute to a wide range of factors, including expanded anti-violence programs and ongoing police reform. Violence is trending downward nationally as well following a sharp spike during the COVID-19 pandemic.

The report suggests several actions that manufacturers could take to keep their firearms out of the hands of criminals, including through increased oversight of the gun dealers they work with. Manufacturers could also focus on producing safer weapons that aren’t easily modified and fund advertising campaigns to increase public awareness of gun safety.

“I think common sense can get through to people. I think wanting to save the lives of our children can get through to people,” said Kansas City Mayor Quinton Lucas. “Manufacturers could do things tomorrow that would make guns safer and save lives.”