Mangione faced two separate criminal prosecutions: a federal trial and another in a New York state court.
Though he pleaded guilty 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 the trial is scheduled to start on 8 September.
On the steps of the court on Friday, his lawyers argued that because he already pleaded guilty to federal charges, the state case runs afoul of double jeopardy – a constitutional protection that prevents an individual from being prosecuted twice for the same crime.
Mitchell Epner, a lawyer and former federal prosecutor, said: “If a federal prosecution has been completed on a matter, the state cannot prosecute the matter on those same facts.”
New York’s state constitution prohibits double jeopardy, which could have a knock-on effect on Mangione’s upcoming trial.
Mangione’s lawyer Karen Friedman Agnifilo said they had already filed a motion explaining why the state charges should be dismissed.
She added that Mangione has accepted “full responsibility” for Thompson’s death.
