NEW YORK — As the first anniversary of the death of UnitedHealthcare CEO Brian Thompson approaches, the man accused in his murder is preparing for a crucial court battle. The defendant seeks to prevent prosecutors from presenting evidence they claim ties him to the crime.

Luigi Mangione, 27, will face hearings starting Monday as he attempts to stop the Manhattan District Attorney’s Office from introducing items seized during his arrest in the pending state murder trial, which has yet to be scheduled.

Among the items in question is a 9 mm handgun that prosecutors allege matches the weapon used in the December 4, 2024, killing. They also point to a notebook in which Mangione purportedly outlined his plan to “wack” a health insurance executive.

Having successfully challenged state terrorism charges in September, Mangione’s defense team is now focusing on alleged unconstitutional actions that they argue compromised his arrest and jeopardize his right to a fair trial.

The defense claims the gun and other evidence should be inadmissible because police did not have a warrant to search the backpack where the items were discovered. Additionally, they argue that some of Mangione’s statements to police, including allegedly providing a false name, should be suppressed because he was questioned before being informed of his 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.

The Manhattan District Attorney’s Office has quoted extensively from Mangione’s handwritten 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.”

Mangione 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.

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.

Court officials say the hearings beginning Monday could take more than a week. If that holds, Mangione is almost certain to be in court on the anniversary of Thompson’s death on Thursday.

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. Police say “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.

The Associated Press contributed to this report.