Manhattan prosecutors say defendant is stalling on psychiatric defense in high‑profile murder case

State prosecutors told a Manhattan judge that defendant Luigi Mangione is stalling on whether he will rely on a psychiatric defense in the high‑profile murder case accusing him of fatally shooting UnitedHealthcare CEO Brian Thompson.

In a letter to Judge Gregory Carro, Assistant District Attorney Joel Seidemann said Mangione, 27, has missed an Aug. 25 deadline to disclose whether he intends to assert a psychiatric or related diminished‑capacity defense, a move prosecutors contend has added to delays in scheduling a trial. "Unnecessary delay thwarts the timely search for truth and erodes public confidence in the justice system," Seidemann wrote. "Pushing back the trial would deprive the People of their day in court at a time when the events are fresh in the witnesses’ memories."

Mangione's lawyers have declined to provide the disclosure, arguing that revealing whether they will use a psychiatric defense would "compromise" his strategy in a separate federal prosecution in which he faces possible death‑penalty exposure, according to court filings cited by prosecutors. That federal case and the state murder case remain on separate tracks, and Judge Carro has not yet set a trial date in the Manhattan matter.

The dispute centers on pretrial disclosure rules and timing, with prosecutors saying the lack of clarity hampers their ability to prepare and could force witnesses to testify long after the events in question. Defense counsel has argued that revealing mental‑health strategy in state court could prejudice Mangione's defense in federal court, where different stakes and procedural issues apply.

The killing of Brian Thompson drew national attention because of Thompson’s role as chief executive of UnitedHealthcare and the unusual overlap of state homicide and federal death‑penalty proceedings in a single defendant's legal posture. Court records show both state and federal prosecutors are navigating competing priorities as they press their respective cases.

Legal experts said defendants who intend to raise an insanity or diminished‑responsibility defense typically must provide notice to the prosecution under many state and federal rules, a disclosure designed to allow time for mental‑health evaluations and to give prosecutors an opportunity to prepare. Courts often balance the prosecution’s need for timely notice against defense claims that premature disclosure could harm strategy in related proceedings.

Seidemann asked the court to compel Mangione to make the disclosure or to enforce scheduling to prevent further delay. The filings do not say whether defense counsel has proposed an alternative timetable or whether they have sought protective measures to limit how any disclosed psychiatric information could be used in the federal case.

A federal death‑penalty indictment remains pending against Mangione in a separate jurisdiction. Defense attorneys have repeatedly warned that cross‑use of statements or evidence between the state and federal cases could prejudice their client in the capital case, an argument that the defense says justifies withholding certain disclosures.

Judge Carro will consider the prosecution's request and the defense's objections at upcoming proceedings. No trial date has been entered, and court officials have given no timeline for resolution of the disclosure dispute.

The resolution of the disclosure dispute could determine the scheduling of a state trial and affect how both the state and federal cases proceed. Prosecutors pressed that timely adjudication is essential to preserve witness testimony and public confidence, while defense attorneys emphasized the potential consequences for Mangione’s federal defense if certain pretrial information is publicly disclosed or shared across jurisdictions.

Both sides are expected to appear in court for further arguments on the matter. The Manhattan District Attorney’s Office declined additional comment beyond the filing, and Mangione’s defense team did not immediately respond to requests for comment.