NEW YORK (AP) — Luigi Mangione appeared in court Monday seeking to bar evidence from his state trial over the killing of UnitedHealthcare CEO Brian Thompson, including the gun that authorities say matches the one used in the brazen New York City attack.

Among the evidence Mangione’s lawyers want to prevent the Manhattan District Attorney’s Office from presenting to jurors are a 9 mm handgun that prosecutors say matches the one used in the Dec. 4, 2024, killing and a handwritten notebook in which they say Mangione described his intent to “wack” a health insurance executive.

After getting state terrorism charges thrown out in September, the defense lawyers are zeroing in on what they say was unconstitutional conduct that tainted his arrest and threatens his right to a fair trial.

They contend that the gun and other items should be excluded because police lacked a warrant to search the backpack in which they were found. They also want to suppress some of Mangione’s statements to police, such as allegedly giving a false name, because officers started asking questions before telling him he had a right to remain silent.

Eliminating the gun and notebook would be critical wins for Mangione’s defense and a major setback for prosecutors, depriving them a possible murder weapon and evidence they say points to motive. Prosecutors have quoted extensively from Mangione’s diary in court filings, including his praise for Unabomber Ted Kaczynski.

In it, prosecutors say, Mangione mused about rebelling against “the deadly, greed fueled health insurance cartel” and said killing an industry executive “conveys a greedy bastard that had it coming.”

Court officials say the hearings could last more than a week, meaning they would extend through Thursday’s anniversary of the attack.

Mangione was allowed to wear normal clothing to the hearings instead of a jail uniform. He entered the courtroom Monday in a gray suit and a button-down shirt with a checkered or tattersall pattern. Court officers removed his handcuffs to allow him to take notes.

The prosecution’s first witness, Sgt. Chris McLaughlin of the New York City Police Department’s public affairs office, testified about efforts to disseminate surveillance images of the suspect to the news media and on social media in the hours and days after the shooting.

To illustrate the breadth of news coverage during the five-day search for the shooter, prosecutors played a surveillance video of the shooting that aired on Fox News Digital, footage from the network of police divers searching a pond in Central Park and clips from the network that included images of the suspected shooter that were distributed by police.

Mangione looked up at a courtroom monitor as video of the shooting played, but he didn’t appear to have any reaction.

A few dozen Mangione supporters watched the hearing from the back of the courtroom. One wore a green T-shirt that said: “Without a warrant, it’s not a search, it’s a violation.” Another woman held a doll of the Luigi video game character and had a smaller figurine of him clipped to her purse.

Mangione, 27, has pleaded not guilty to state and federal murder charges. The state charges carry the possibility of life in prison, while federal prosecutors are seeking the death penalty. Neither trial has been scheduled yet.

Mangione’s lawyers want to bar evidence from both cases, but this week’s hearings pertain only to the state case. The next hearing in the federal case is scheduled for Jan. 9.

Defense lawyer Marc Agnifilo told a judge in an unrelated matter last week that Manhattan prosecutors could call more than two dozen witnesses.

Thompson was killed as he walked to a Manhattan hotel for his company’s annual investor conference. Surveillance video showed a masked gunman shooting him from behind.

Prosecutors have claimed “delay,” “deny” and “depose” were written on the ammunition, mimicking a phrase used to describe how insurers avoid paying claims.

Mangione, the Ivy League-educated scion of a wealthy Maryland family, was arrested five days later at a McDonald’s in Altoona, Pennsylvania, about 230 miles (about 370 kilometers) west of Manhattan.

Prosecutors in the state case have not responded to the defense’s written arguments.

An officer searching a backpack found with Mangione was heard on a body camera recording saying she was checking to make sure there “wasn’t a bomb” in the bag. His lawyers argue that was an excuse “designed to cover up an illegal warrantless search of the backpack.”

Federal prosecutors, fighting similar claims in their case, have said in court filings that police were justified in searching the backpack to make sure there were no dangerous items. His statements to officers, federal prosecutors said, were made voluntarily and before he was taken into police custody.