A man accused of impersonating a federal agent in a bid to allegedly free Luigi Mangione, the man accused of gunning down the CEO of United Healthcare in 2024, has been arrested.

Mark Anderson, 36, is accused of going to the New York jail where Mangione is being housed and allegedly posing as an FBI agent, a criminal complaint states. He allegedly said he had paperwork that had been "signed by a judge" to free the accused killer.

Though the complaint does not name Mangione, a law enforcement source told the BBC that Anderson allegedly sought to free him.

He appeared before a judge on Thursday but has not entered a plea. The BBC has contacted an attorney said to be representing him.

Anderson approached the intake area of the Metropolitan Detention Center in Brooklyn on Wednesday and is accused of telling officers that he was an FBI agent, the criminal complaint states. He said he had paperwork "signed by a judge" to authorise the release of an inmate.

When officers asked him for credentials, Anderson provided a Minnesota driver's licence, claimed be in possession of weapons, and "displayed and threw" what authorities described as "numerous documents" at jail staff, according to the complaint.

Bureau of Prisons officials then detained Anderson and searched his bag, where they found a large "barbecue type fork" with two prongs and a tool that resembles a pizza cutter.

The suspect had travelled to New York City for a job opportunity from Mankato, Minnesota, and had been working at a local pizzeria, according to the law enforcement source.

Anderson is facing a charge of impersonating an officer.

Mangione has been held at the Brooklyn jail since 2024. He was arrested in a McDonalds in Pennsylvania after a multi-state manhunt and then extradited to New York.

He faces both state and federal charges in the killing of United Healthcare CEO Brian Thompson and has pleaded not guilty.

Since his arrest, Mangione has attracted a legion of supporters both online and at his court appearances. The killing also launched a debate in the US over healthcare costs.

Jury selection for Mangione's highly anticipated federal trial is currently scheduled for September.