• Police said they found a "ghost gun" on the UnitedHealthcare CEO shooting suspect.
• Ghost guns are untraceable firearms that can be assembled at home, raising safety concerns.
• Elected officials are cracking down on the sale of such weapons to curb their accessibility.

Police say a weapon they found on UnitedHealthcare CEO shooting suspect Luigi Mangione could be a 3D printed ghost gun.

Ghost guns are firearms assembled at home using parts that were purchased individually. Sometimes, those components are made using a 3D printer. It's legal to buy the parts and use them to make your own gun, but laws prohibit the sale or transfer of ghost guns to another person.

Mangione "was in possession of a ghost gun that had the capability of firing a 9mm round," Joe Kenny, the New York Police Department's chief of detectives, told reporters on Monday.

He added that it "may have been made on a 3D printer"; there's no confirmation that it was the same gun used to kill Brian Thompson.

Mangione is being held without bail, and a lawyer for him has not yet been publicly identified.

Both authorities and gun safety groups have raised concerns about ghost guns, which are accessible online in kits. More than 25,000 privately made firearms were recovered by US law enforcement agencies in 2022, according to the DOJ.

In 2022, New York City officials filed a lawsuit against five ghost gun retailers over their sales to residents. Mayor Eric Adams eventually came to an agreement with at least four of the companies that would stop the sale of ghost guns in NYC.

It's unclear if the firearm Pennsylvania police say they recovered from Mangione is technically a ghost gun, said Kris Brown, the president of the gun safety group Brady.

They'll know for sure once investigators examine the weapon to see if any of its component parts have serial numbers. Only if there are no serial numbers is it a ghost gun, meaning entirely unregulated and untraceable, Brown told Business Insider.

Mangione may have printed the plastic portions of his gun, but he likely purchased the metal components, she said. Under current law, if you buy these components as part of a kit, you need a background check, Brown said.

These include the slide, the thread for the barrel, and the trigger mechanism; all are easily acquired through mail-order companies that advertise online.

Currently, some states require serial numbers for separately sold metal components, and some do not, Brown said.

Brady advocates for gun-control legislation, including the 2022 rule issued by the Biden-Harris administration regulating the sale of ghost gun kits."That bill has been very effective," she said. "Without it, it would have been lawful for a shooter to buy a kit and assemble an entire gun in minutes." In 2023, there was a drop in ghost gun recoveries by police nationwide, Mark Collins, Brady's director of federal policy, said.

Brady is pushing next for passage of the Ghost Guns and Untraceable Firearms Act, which would set a federal standard requiring background checks and the serialization of build-it-yourself gun parts.