Defense attorneys for Luigi Mangione, facing charges in the killing of UnitedHealthcare CEO Brian Thompson, and federal prosecutors in New York discussed a possible plea deal in the case ahead of a hearing Monday, but talks fell apart, according to two sources familiar with the matter.  

It is unclear how close the two sides came to a possible plea agreement before negotiations ended, according to the sources. It is unknown whether there will be an effort to resume discussions. 

The pretrial hearing in the case scheduled for Monday in Manhattan federal court is still expected to take place to discuss plans for an upcoming trial.

Mangione is facing both state and federal charges for Thompson's murder in December 2024. He has pleaded not guilty in both cases.

A spokesman for the U.S. Attorney for the Southern District of New York declined to comment to CBS News on the plea negotiations. CBS News has reached out to Manhattan District Attorney Alvin Bragg.  

NBC News New York first reported Thursday that Mangione's attorneys had talks with federal prosecutors about a possible plea deal in advance of the scheduled court hearing on Monday, July 6, citing sources familiar with the matter.

Mangione's attorneys had said in a statement to CBS News earlier Thursday that the report was "troubling."

"This information attributed to 'anonymous sources' is part of a troubling, deliberate pattern by prosecutors and law enforcement to prejudice Luigi, manipulate public opinion, and violate his constitutional right to a fair trial and impartial jury," defense attorney Karen Friedman Agnifilo said. "Every defendant in America is presumed innocent until proven guilty, including Luigi, who has to fight the same charges twice."

Discussions between prosecutors and defense attorneys prior to trial, including discussions about plea agreements, are common, legal experts told CBS News.

"They're going to have a conversation about whether or not they will do a deal. It is not at all uncommon to have a conversation about a potential plea deal throughout the process," CBS News legal analyst Jessica Levinson said.

"Generally, the defense will say, 'Hey, can we plead this out,' and prosecutors will say, 'Here's what we can offer,'" said former Palm Beach County State Attorney Dave Aronberg.

Plea agreements can be negotiated all the way up until trial, as in the recent case of Bryan Kohberger, who pleaded guilty last July to the murders of four University of Idaho students as part of a plea deal that spared him from facing the death penalty.

"To paraphrase Lenny Bruce, 'In the halls of justice, justice is often done in the halls,'" Aronberg said.

Earlier this month, Mangione's attorneys said they might seek a psychiatric defense for Mangione in his New York state trial. The following day, on June 18, Mangione's attorneys abruptly withdrew the notice of their intent to argue an "extreme emotional disturbance."

Mangione's case has garnered outsized attention from around the world since he was accused of the December 2024 killing of Thompson outside a healthcare industry conference in Midtown Manhattan. 

The trial in the state case is set to begin in September, followed by the federal interstate stalking trial scheduled to begin in November.