A Minnesota man has been accused of impersonating an FBI agent to attempt to free accused health insurance CEO killer Luigi Mangione from a Brooklyn prison, while carrying a barbecue fork and a pizza-cutter blade, court records show.

Mangione, 27, faces a death penalty murder charge for allegedly killing UnitedHealth Group CEO Brian Thompson in Manhattan in 2024.

Public officials condemned the shocking killing, but Mangione became a folk hero to some Americans who decry steep healthcare costs and insurance company practices. He has pleaded not guilty to murder and other charges in separate state and federal cases.

Brooklyn federal prosecutors on Wednesday accused Mark Anderson, 36, of Mankato, Minnesota, of showing up at the Metropolitan Detention Centre and telling prison staff that he was an FBI agent with paperwork signed by a judge authorising the release of an inmate.

The criminal complaint does not identify the inmate, but a law enforcement source, who was not authorised to speak publicly, said it was Mangione. Anderson was working at a pizzeria after arriving in New York, the source said.

Information on a legal representative for Anderson was not immediately available on Thursday.

Prosecutors said Anderson provided his Minnesota driver’s license when asked to show credentials and told prison guards he had weapons. Guards arrested and searched Anderson and found a barbecue fork and a round pizza-cutter blade in his backpack, according to the complaint.

He threw documents at the guards that appeared to be unspecified claims against the US Department of Justice, according to the complaint.

Mangione was arrested in Altoona, Pennsylvania, in December 2024 after a five-day manhunt that followed Thompson’s murder. Police say they found a 3D-printed handgun, a silencer and a note criticising the US healthcare system in his backpack.

Mangione’s pretrial hearings have been packed with spectators, many of whom voice support for him, and demonstrators have gathered outside courthouses to protest against health insurance industry practices.

He is set to stand trial in Manhattan federal court in September on charges including murder with a firearm and stalking. Mangione’s lawyers have asked to dismiss the indictment or prevent the death penalty from being sought.

Mangione has pleaded not guilty to murder, weapons and forgery charges in a separate case in state court in Manhattan. No trial date has been set.