Luigi Mangione has pleaded guilty to federal charges that he stalked United Healthcare boss Brian Thompson across state lines, resulting in his 2024 death.

The 28-year-old appeared in a Manhattan courtroom on Friday, where he agreed to admit to both of his two federal stalking charges. He could face up to a lifetime in prison.

Though the federal matter is drawing to close, Mangione also faces a slew of separate charges in New York state, including second degree murder, for which he’s set to go to trial next month. The actual sentencing will happen in December.

His admission today may throw a wrench in the state trial, as Mangione’s lawyers try to argue he cannot be prosecuted again with the same evidence.

Mangione on Friday pleaded guilty to two federal charges of stalking resulting in death that carry a maximum penalty of life in prison without parole. Federal prosecutors say the 28-year-old travelled across state lines and used surveillance to kill the healthcare boss.

He has not made a sentencing deal with the prosection, just agreed to plead guilty. The defendant had previously pleaded not guilty to all charges.

The US government originally charged Mangione with four crimes. But federal judge threw out two of the counts in January, including federal firearms charges that carried the death penalty as a possible sentence.

Federal prosecutors brought the stalking charges against Mangione, alleging he travelled between states and carried out electronic surveillance with the intention of killing or harming Thompson. Prosecutors allege those actions resulted in Thompson’s death.

Mangione faced two separate criminal prosecutions – in New York state court as well as federal court – over the killing of Thompson.

Though he pleaded guilty Friday in federal court, he still faces eight state charges, including second degree murder. He has pleaded not guilty to all eight of those charges, and he is due to stand trial starting 8 September.

His lawyers have previously argued that Mangione should not be tried in both state and federal court.

But Mangione’s guilty plea in the federal case could have a cascading effect on the upcoming proceedings in state court. It could open the door for defence lawyers to argue the state case runs afoul of double jeopardy – a constitutional protection that prevents an individual from being prosecuted twice for the same crime.

New York’s state constitution has its own prohibition on double jeopardy, which also could have a knock-on effect on Mangione’s upcoming trial.

“If a federal prosecution has been completed on a matter, the state cannot prosecute the matter on those same facts,” said Mitchell Epner, a lawyer and former federal prosecutor.

Mangione currently faces eight total felony charges in New York state court: second degree murder, possession of a forged instrument (for alleged fake driver’s license), and six counts of criminal possession of a weapon, all of which he denies.

The 28-year-old was originally charged with three additional counts – first degree murder in furtherance of terrorism, second degree murder as an act of terrorism, and a count of criminal possession of a weapon – but those have since been dropped by a judge.

If convicted, Mangione faces 25 years up to life in prison for the state charges.

When the US Department of Justice first filed federal charges against Mangione in December 2024, they included one count of using a firearm to commit murder, which carries a maximum penalty of death.

But in January, a federal judge dismissed that charge – the only capital offense out of all state and federal charges – taking the possibility of the death penalty off the table for Mangione.

Judge Margaret Garnett also dismissed one federal count related to discharging a weapon with a silencer, leaving just two federal charges remaining, both related to interstate stalking.

None of the state charges against Mangione can carry the death penalty because New York state declared capital punishment unconstitutional in 2004.