Luigi Mangione has arrived in New York where he faced four new federal charges and the possibility of the death penalty.
The accused CEO killer was charged with murder using a firearm, two charges of stalking and a charge of using an illegal gun silencer, according to a criminal complaint.
These are in addition to previous state murder and terrorism charges.
If convicted, the charge of murder by firearm could bring the possibility of the death penalty but federal prosecutors have not said whether they will pursue it or not.
Federal and state authorities will now both move forward with parallel proceedings, with the state charges expected to go to trial first.
Mangione had been held in Pennsylvania since his arrest on December 9 but at a hearing on Thursday morning he agreed to be returned to New York and was immediately turned over to at least a dozen New York Police Department officers.
First sent to Long Island, he then was flown to a Manhattan heliport, where he was marched up a pier surrounded by armed officers, New York City Mayor Eric Adams and Police Commissioner Jessica Tisch.