The retraction on Thursday came a day after Mangione's lawyers told Judge Gregory Carro that they planned to pursue a defence involving claims that the 28-year-old Ivy League graduate was suffering from extreme emotional disturbance at the time of the December 4, 2024 killing.
A message seeking comment was left with a spokesperson for Mangione's lawyers. The Manhattan district attorney's office, which is prosecuting the state case, declined to comment.
Mangione's lawyers had faced a Thursday deadline to provide prosecutors with information to support the emotional disturbance claim. Also on Thursday, a transcript of a secret hearing held on the matter on June 3 was made public after Carro ordered it unsealed.
If Mangione were to have gone through with the extreme emotional disturbance defence, he would have effectively been admitting that he killed Thompson but did so because of mitigating circumstances. It wouldn't have absolved him of responsibility, but could have led to less time in prison.
If a jury accepts the defence, it is obligated to convict a defendant of manslaughter, which is punishable by up to 25 years in prison, instead of murder, which carries a potential life sentence.
In a letter to Carro on Thursday, Mangione lawyer Karen Friedman Agnifilo said the defence "respectfully withdraws" its notice under New York's psychiatric defence statute.
Mangione, 28, has pleaded not guilty to state and federal charges. His state trial is scheduled to start September 8. His federal trial, which involves stalking charges, is set to begin on October 13.
At Wednesday's hearing, Friedman Agnifilo protested Carro's decision to unseal materials related to his psychiatric defence, saying it will be "prejudicial to his defence to the exact same facts" in his federal case, where an extreme emotional disturbance defence isn't allowed.
An emotional disturbance defence is not the same as a not guilty by reason of insanity defence, which would allow a defendant to go to a psychiatric facility instead of prison.
Thompson, 50, was killed as he walked to a Manhattan hotel for UnitedHealth Group's annual investor conference. Surveillance video showed a masked gunman shooting him from behind. Police say "delay," "deny" and "depose" were written on the ammunition, mimicking a phrase used to describe how insurers avoid paying claims.
Mangione, an Ivy League graduate from a wealthy Maryland family, was arrested five days later at a McDonald's in Altoona, Pennsylvania, about 370km west of Manhattan.Â
At a hearing in May, Carro ruled that a gun and notebook that prosecutors say link Mangione to the killing can be used as evidence against him.
The gun, a 3D-printed pistol, matches the one used to kill Thompson, prosecutors said. The notebook describes wanting to "wack" a health insurance executive and rebelling against "the deadly, greed fuelled health insurance cartel".
