Luigi Mangione plea talks raise showdown over Brian Thompson murder trial

Manhattan prosecutors are signaling they could fight a federal plea deal for Luigi Mangione if it threatens to derail his upcoming New York murder trial in the killing of UnitedHealthcare CEO Brian Thompson.

In a newly unsealed letter reviewed by Fox News Digital, the Manhattan District Attorney's Office said it is aware of reports that Mangione could seek a guilty plea in his separate federal case before the state trial begins.

Prosecutors warned that if such a deal would interfere with New York's prosecution, they could ask the federal judge to take that into account before accepting it.

The filing follows a June hearing in federal court, where U.S. District Judge Margaret Garnett pushed Mangione's federal trial to January 2027, clearing the way for his New York murder trial to move forward first.

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Mangione, 28, has pleaded not guilty in both the state and federal cases stemming from the December 2024 killing of UnitedHealthcare CEO Brian Thompson, who was shot outside a Manhattan hotel as he headed to a conference.

"If a proposed federal guilty plea would operate to defeat a just outcome in the state prosecution, the People could advise the federal district court of that consequence, and the court should consider that fact in deciding whether to accept the plea," Assistant District Attorney Joel Seidemann wrote in the July 2 letter.

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Prosecutors added that the court should also consider any opposition from Thompson's family before accepting such a plea.

The letter marks the clearest sign yet that Manhattan prosecutors are prepared to push back against any deal they believe could keep the state's high-profile murder case from ever reaching a jury.

The DA's office said it has already shared its position with federal prosecutors and Mangione's defense team.

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Prosecutors argued that any resolution should reflect "the seriousness of defendant's offenses," "the loss of an innocent life," the impact on Thompson's family and New York's interest in prosecuting the homicide.

The dispute comes after reports surfaced in June that Mangione's legal team and federal prosecutors had discussed a possible plea deal but failed to reach an agreement.

Mangione attorney Karen Friedman Agnifilo blasted information attributed to anonymous sources at the time as "a troubling, deliberate pattern by prosecutors and law enforcement to prejudice Luigi."

A spokesperson for the U.S. Attorney's Office for the Southern District of New York previously declined to comment on the reported negotiations.

At a June 29 hearing, Garnett delayed Mangione's federal trial after concluding there was no practical way for his attorneys to prepare for two high-profile trials at the same time.

During that hearing, Agnifilo confirmed Mangione's New York murder trial remained on track to begin Sept. 8 and said the defense had been told there would be no delays.

"We've been told that no requests for adjournments will be granted and to be ready on that date," Agnifilo told the court.

The judge said there was simply no realistic way to move both cases forward at once.

"It's simply impossible for us to be moving through the jury selection process in this case while the defendant and his counsel are fully occupied actually conducting the state trial," the judge said. She rescheduled federal jury selection for Jan. 5, 2027, with opening statements set for Jan. 25.

Under the revised schedule, about 800 prospective jurors will complete written questionnaires in early December before in-person jury selection begins.

Manhattan prosecutors also argued New York should get the first opportunity to try Mangione because he was extradited there on the state case before he was later transferred into federal custody. Prosecutors argued that the transfer did not change New York's priority to prosecute him first.

Prosecutors allege Mangione fled the city and was arrested five days later at a McDonald's in Altoona, Pennsylvania. 

Fox News Digital's Michael Ruiz contributed to this report.