A New York judge will decide Monday if evidence found in Luigi Mangione's backpack during his arrest can be used during his state trial.

Mangione is being tried on both federal and state charges for the December 2024 shooting death of UnitedHealthcare CEO Brian Thompson. He pleaded not guilty in both cases.

The judge is expected to rule on the defense's bid to suppress evidence found in the bag, including a 3D-printed gun, silencer and a notebook. 

Mangione's lawyers say their client was unlawfully searched when he was arrested at a McDonald's in Altoona, Pennsylvania. The defense said law enforcement should've obtained a warrant before looking in the backpack. 

Prosecutors say the search was legal and part of standard police procedure. They said the backpack was searched after Mangione gave a false identity to officers.

The judge in Mangione's federal case ruled in January that the backpack evidence can be admitted. 

Legal expert weighs in 

Legal expert Richard Schoenstein, who isn't affiliated with the case, said this hearing is critical for the trial.

"The gun and the writing that suggest a motive are pretty much the best evidence in the case," he said.

When a person is taken into custody, police are able to pat them down. But what makes this situation tricky is that Mangione wasn't wearing the backpack when he was arrested. 

"If you have a bag on you, generally that's fair game too. But what makes it a little bit different here is that the bag was apparently sitting on the table. It wasn't touching the person of Luigi Mangione. So there's a question of whether those principles of search apply," Schoenstein said. 

State trial pushed back

During his last federal hearing, a judge pushed back the start of Mangione's federal interstate stalking trial.

Later that day, the state trial was pushed back from June 8 to Sept. 8. Jury selection for his federal trial will start on Oct. 5, with opening statements either Oct. 26 or Nov. 2.

Defense attorneys previously said they needed more time because they are representing Mangione in multiple cases at the same time. 

Prosecutors argued the real reason the defense wanted to postpone was because the lawyers have another high-profile client. 

Mangione's lawyers  – Jacob Kaplan, Marc Agnifilo and Teny Geragos – confirmed in February they will be representing Harvey Weinstein in his sexual assault case. That case ended in a mistrial Friday.