Luigi Mangione’s lawyers will ask a judge to toss evidence seized during his arrest last year, arguing that police illegally seized a handgun and a diary from his backpack that prosecutors say showed he planned to kill a health care executive.

In a multiday hearing starting in New York state court on Monday, lawyers for Mangione will argue that the local police officers who arrested him at a McDonald’s in Altoona, Pennsylvania, violated his legal rights by searching his backpack without a warrant and questioned him for 20 minutes before reading him his constitutional rights.

The 27-year-old is accused of shooting and killing UnitedHealth Group Inc. executive Brian Thompson outside a Manhattan hotel one year ago this week. The result of the hearing could impact the strength of the murder case and shape what evidence prosecutors will be allowed to introduce at trial.

Attempts to throw out evidence in criminal cases are common, but rarely succeed in substantially limiting the scope of a case. If successful, Mangione could have a stronger hand in potential plea negotiations with prosecutors, who have charged him with second-degree murder and other crimes.

The judge weighing the request earlier this year tossed out first-degree murder charges against Mangione. He also faces federal murder charges that could result in a death penalty if he is convicted.

Prosecutors say they have compiled an unassailable trove of evidence against Mangione, including videos of him at the crime scene outside the Hilton Hotel on Sixth Avenue in Manhattan. The material from the Altoona search contains a so-called manifesto, a key document in which the former Ivy League graduate expressed his desire to kill an insurance executive and lauded “Unabomber” Ted Kaczynski. His lawyers argue his backpack was illegally searched, and that anything in it shouldn’t be used as evidence.

The case has drawn intense national interest as Mangione has been cheered by fans who say he expressed their rage at the health care system, while government officials, including President Donald Trump, have linked him to “left-wing” extremism.

Ahead of the hearing, Mangione’s lawyers, Karen Friedman Agnifilo and her husband Marc Agnifilo, laid out in court documents a detailed timeline of his arrest in Altoona and the conduct of officers last December.

Officer Joseph Detwiler arrived at the McDonald’s that morning and told Mangione that someone had called the police because they thought he was suspicious.

“Even though Patrolman Detwiler had already decided that Mr. Mangione was the New York shooter, he told Mr. Mangione, as a pretext for the police interaction, that they were there because Mr. Mangione had been at the McDonald’s for 40 minutes,” Friedman Agnifilo said.

Detwiler asked Mangione what he was doing in New York, but before he could respond the patrolman asked Mangione to stand up and put his hands on top of his head, with Detwiler “grabbing and lifting” Mangione’s right wrist and then frisking him.

Another officer, Christy Wasser, then searched Mangione’s backpack, without a warrant, where they found the 9 mm handgun and the manifesto. Friedman Agnifilo said the police didn’t obtain a search warrant for another seven hours.

“Realizing she had made a potentially devastating mistake by thoroughly searching the backpack of a murder suspect in a significant New York press case without a warrant, Wasser suddenly stated that she was searching through the backpack at McDonald’s to make sure there ‘wasn’t a bomb or anything in here,”’ Friedman Agnifilo wrote.

Mangione has already scored a surprise victory from New York judge Gregory Carro in the state murder case. In September, Carro tossed first-degree murder charges that classified the crime as an act of terrorism, ruling Mangione didn’t intend to terrorize or intimidate UnitedHealth employees.

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