The man charged with murdering UnitedHealth Group Inc. executive Brian Thompson on a Manhattan sidewalk last week was arrested with a “ghost gun” in his backpack, refocusing attention on the hard-to-trace weapons and their lethal power.

A black pistol found in the backpack of UnitedHealthcare shooting suspect Luigi Mangione appeared to have been a ghost gun, police said.

Police say the suspect had a ghost gun, possibly made with a 3D printer, when he was arrested on Monday. Here's what to know about the increasingly widespread weapons and efforts to regulate them.

WASHINGTON (AP) — The brazen killing of UnitedHealthcare’s CEO was likely carried out with a ghost gun, one of the nearly untraceable weapons that can be made a home, police said Monday.

Court papers said the gun believed to be used in UHC CEO Brian Thompson's shooting likely was a ghost gun, an untraceable firearm also found in Connecticut.

"He has constitutional rights and that's what he's doing" in challenging the interstate transfer, his attorney, Thomas Dickey, told reporters in Pennsylvania.

Police said Luigi Mangione, the man charged in the killing of UnitedHealthcare CEO Brian Thompson, appears to have had a ghost gun, a weapon that can be made using a 3D printer.

The suspect in the killing of UnitedHealthcare’s CEO likely was motivated by his anger with what he called “parasitic” health insurance companies and a disdain for corporate greed, a law enforcement bulletin obtained by The Associated Press said.