The legal case against Luigi Mangione expanded on Thursday, with the federal government filing four criminal charges against him, including one punishable by death.

Mr Mangione, who is accused of killing UnitedHealthcare CEO Brian Thompson earlier this month, arrived by helicopter in Manhattan in the afternoon after being extradited from Pennsylvania.

He disembarked in an orange jumpsuit and handcuffs and, surrounded by officials and armed guards, walked before cameras and journalists to the van that would take him to court.

The 26-year-old will remain behind bars as his lawyers said that they would not yet present an application for bail.

During a 15-minute hearing, where he appeared wearing a blue sweater and khaki pants with his feet shackled, a judge read out loud the four federal charges against him.

Mr Mangione’s hearing was packed with reporters, members of the public and court staff. Several people outside protested in support of him, holding a sign saying: “Luigi freed us”.

The level of protection being provided to Mr Mangione is equivalent to what visiting diplomats and dignitaries typically receive when they visit New York, Felipe Rodriguez, a former detective sergeant who served on the NYPD for 21 years, told the BBC.

Mr Rodriguez, who now teaches at the John Jay College of Criminal Justice in New York City, said Mr Mangione was receiving “extreme protective executive protection” – or what officers there simply call “protecting the package”.

New York Mayor Eric Adams was part of a throng police officials who met Mr Mangione’s chopper when it landed in Manhattan.

Mr Mangione’s day began with a hearing in Pennsylvania, where he was arrested on 9 December, to discuss extraditing him back to New York, where the shooting occurred. He appeared shackled in the orange jumpsuit, and afterwards was taken by plane to an airport on Long Island, New York, then to Manhattan.

Mr Mangione was arrested at a McDonald’s in Altoona, Pennsylvania, five days after Mr Thompson, the UnitedHealthcare CEO, was shot and killed. He was found with a fake ID and so-called “ghost gun”, police have said.

During the New York hearing on Thursday, Mr Mangione sat between his two lawyers – Karen Friedman Agnifilo, and her husband, Mark Agnifilo, who also is representing rapper Sean “Diddy Combs” in his sex trafficking case.

Mr Mangione nodded along during the hearing as New York Magistrate Judge Katherine Parker read him his rights, including the right to remain silent.

She also read the charges against him: two counts of stalking, a firearms offense, and murder through use of a firearm, which opens up the possibility of the death penalty.

The proceedings were largely standard, but Mr Mangione’s lawyer, Ms Agnifilo, who appeared in the courtroom on crutches, asked prosecutors to clarify how many cases Mr Mangione would face.

He already was indicted on state charges in New York, including first-degree murder in furtherance of terrorism, and now also faces federal charges.

Ms Agnifilo told the court that the overlapping cases – and a murder charge against Mr Mangione that makes him eligible for the death penalty – were “confusing” and “highly unusual”.

“I’ve never seen anything like what is happening here” in 30 years of practicing law, she said.

The suspect is being held at Metropolitan Detention Center (MDC) Brooklyn.

New York prosecutors began to share evidence in their case against Mr Mangione with a grand jury last week. The evidence against him includes a positive match of his fingerprints with those discovered at the crime scene, New York Police Commissioner Jessica Tisch said.

According to New York District Attorney Alvin Bragg, the suspect arrived in New York City on 24 November, staying in a Manhattan hostel while using a fake ID before carrying out the attack against Mr Thompson 10 days later.

In addition to the ghost gun – a gun assembled from untraceable parts – and fake ID, a passport and a handwritten document indicating “motivation and mindset” also were found on Mr Mangione when he was arrested, police said.