Alleged CEO killer Luigi Mangione has withdrawn his psychiatric defence plan one day after putting it forward.

Mangione’s lawyers have now informed the judge in the New York state murder case they will not go ahead with their plan to argue Mangione killed UnitedHealthcare’s chief executive while suffering an extreme emotional disturbance.

WATCH THE VDIEO ABOVE: Luigi Mangione reverses psychiatric defence decision.

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The notice came in a court filing one day after a hearing in which Mangione’s lawyers had indicated they would argue a psychiatric defence.

His lawyers could not immediately be reached for comment. The Manhattan District Attorney’s office declined to comment.

Judge Gregory Carro said at a hearing on Wednesday he planned to unseal records related to an affirmative defence available to New York state criminal defendants charged with murder, in which the accused admits to the charged conduct but argues they should not be held fully criminally liable because he or she acted while experiencing a mental health episode.

However, in light of the defence’s withdrawal, Carro said on Thursday he would keep those records sealed.

If a jury finds a defendant has proved by a preponderance of evidence he acted because of an extreme emotional disturbance, the crime is reduced from murder to manslaughter, which carries far less prison time.

Experts had previously told CNN a psychiatric defence would be challenging but was likely Mangione’s best argument given the strength of the evidence against him.

In a key ruling last month, Carro cleared the way for prosecutors to present crucial evidence they contend ties Mangione to the crime scene and could shed light on his motive for the killing.

Mangione has pleaded not guilty to state murder and weapons charges in the December 2024 fatal shooting of UnitedHealthcare CEO Brian Thompson as he walked toward a Midtown Manhattan hotel hosting his company’s annual investors’ conference.

The state trial is slated to begin in September.

Mangione has also pleaded not guilty to federal stalking charges.

‘So, what happened since yesterday?’

Former prosecutor Gary Galperin called the sudden shift in the defence’s strategy “stunning”.

“So, what happened since yesterday?” he queried.

Galperin speculated it is possible Mangione changed his mind and didn’t want to move forward with the defence, or that the defence’s mental health expert retracted.

Mangione’s lawyers had until Thursday to turn over to prosecutors the name of their expert and the expert’s credentials.

Mangione’s lawyers had asked for their discussions about a potential psychiatric defence to remain under seal in part because of the potential impact it could have on prospective jurors.

During a June 3 hearing — which was initially sealed — Mangione’s lawyer Karen Friedman Agnifilo said, according to a transcript that was unsealed on Thursday, “if a defendant goes with an EED defence, they’re essentially admitting publicly that they committed this crime”.

“And due to the high publicity in this case,” she said, “making this public before we know for sure whether we are going with this defence, it prejudices both this case and the federal case because of the extraordinary publicity effecting potential jurors.”

Galperin said: “In such a high-profile case, to put it out there and take it back presents the very same concerns that caused them to ask for the sealing.”