Accused CEO killer Luigi Mangione has been charged with federal murder and stalking crimes in a Manhattan courtroom, the latter which could bring the death penalty if he's convicted.
Federal prosecutors charged Mr Mangione with the federal crime of murder using a firearm, two charges of stalking and a charge of using an illegal gun silencer, according to a criminal complaint.
One of the federal charges, murder by firearm, could bring the possibility of the death penalty if he is convicted.
Federal prosecutors have not said whether they will pursue such a punishment.
The 26-year-old was held without bail following the federal court appearance, capping a whirlwind day that began in Pennsylvania, where he was arrested last week.
Mr Mangione had been expected to be arraigned on a state murder indictment in the killing of UnitedHealthcare CEO Brian Thompson, but the federal charges pre-empted that appearance.
The cases will now proceed on parallel tracks, prosecutors said, with the state charges expected to go to trial first.
That's on top of the state charges filed in New York, which include murder as an act of terrorism.
Mr Mangione, shackled at the ankles and wearing dress clothes, said little during the 15-minute proceeding as he sat between his lawyers in a packed federal courtroom.
The Ivy League graduate nodded as a judge informed him of his rights and the charges against him, occasionally leaning forward to a microphone to tell her he understood.
Mangione had been held in Pennsylvania since his arrest while eating breakfast at a McDonald's in Altoona on December 9.
At a hearing in Pennsylvania on Thursday morning, Mr Mangione agreed to be returned to New York and was immediately turned over to at least a dozen New York Police Department officers who took him to an airport and a plane bound for Long Island.
He then was flown to a Manhattan heliport, where he was walked slowly up a pier by a throng of officers with assault rifles — a contingent that included New York City Mayor Eric Adams and Police Commissioner Jessica Tisch.
Mr Mangione agreed to waive his right to an extradition hearing in Pennsylvania, where he was arrested last week, and was immediately turned over to a group of NYPD officers who led him to a small plane for the New York area.
Handcuffed and in a bright orange jumpsuit, he was escorted off a helicopter that landed in Lower Manhattan by a large group of police officers and New York City Mayor Eric Adams.
A courtroom had been set aside in a Manhattan federal courthouse for Mr Mangione's appearance and an overflow courtroom was designated as a location for people to watch on video in case there are more people than can fit in the courtroom.
Pennsylvania attorney Pete Weeks had said he wanted to turn Mr Mangione over to New York authorities as soon as possible. Mr Weeks said he was willing to put other charges in Pennsylvania on hold.
"He is now in their custody. He will go forth with New York to await trial or prosecution for his homicide and related charges in New York," Mr Weeks said.
Simultaneous state and federal charges
Earlier this week, Manhattan District Attorney Alvin Bragg's office charged Mr Mangione with murder as an act of terrorism.
As New York does not have the death penalty, the charge carries a possible sentence of life in prison without parole.
Mr Mangione's lawyer, Karen Friedman Agnifilo, said it's a "highly unusual situation" for a defendant to face simultaneous state and federal cases.
"Frankly I've never seen anything like what is happening here," said Friedman Agnifilo, a former top deputy in the Manhattan district attorney's office.
She reserved the right to seek bail at a later point and declined to comment as she left the courthouse.
Mr Mangione is accused of ambushing and shooting Brian Thompson on December 4 outside a Manhattan hotel.
The head of UnitedHealthcare, the United States' largest medical insurance company, was walking to an investor conference.
Authorities have said Mr Mangione was carrying the gun used to kill Mr Thompson, a passport, fake IDs and about $US10,000 when he was arrested while eating breakfast at a McDonald's.
Investigators believe he was motivated by anger toward the US health care system and corporate greed.
But he was never a UnitedHealthcare client, according to the insurer.
The killing ignited an outpouring of stories about resentment toward American health insurance companies while also shaking corporate America after some social media users called the shooting payback.
AP/ABC