Lawyers for the defendant accused of gunning down UnitedHealthcare Chief Executive Brian Thompson will no longer argue a psychiatric defence at his state murder trial.

Luigi Mangione's attorneys reversed course a day after telling Judge Gregory Carro that they would try to show he was suffering from "extreme emotional disturbance at the time of the occurrence".

Mangione, 28, has pleaded not guilty in both the federal and state cases against him for the fatal shooting of Thompson in midtown Manhattan at the end of 2024.

The BBC has contacted Mangione's attorneys. The Manhattan district attorney's office declined to comment.

The reversal came ahead of a Thursday deadline Mangione's legal team was facing to provide prosecutors at the Manhattan district attorney's office with information in support of the psychiatric defence claim.

If Mangione had pursued the psychiatric defence, and the jury accepted it, then he could have faced a shorter prison sentence as he might have faced a conviction for manslaughter, instead of murder.

By using a psychiatric defence argument, Mangione would have essentially admitted to killing Thompson with mitigating circumstances, legal expert Richard Schoenstein told CBS.

That argument is different from pleading not guilty by reason of insanity, which typically seeks exoneration and a punishment that includes a psychiatric facility rather than prison.

Mangione appeared in court on Wednesday as the judge spoke about his then-planned psychiatric defence.

His next court date is scheduled for 11 August, before the state trial begins on 8 September.

Mangione is also facing federal stalking charges, which can bring a maximum sentence of life in prison.

He was arrested days after Thompson, a 50-year-old father of two, was shot from behind by a masked gunman on 4 December 2024 as he walked into a Manhattan hotel for an annual investor conference.