A New York judge on Monday rejected arguments from lawyers defending Luigi Mangione, the man accused of assassinating United Healthcare CEO Brian Thomas, who said that a gun and notebook described as a "manifesto" were seized illegally from their client. 

The ruling will allow prosecutors to use the items in Mangione's trial on nine state felony charges, including second-degree murder, NBC News reported. 

Thompson was gunned down on a Manhattan sidewalk Dec. 4, 2024.

Judge Gregory Carro ruled that prosecutors can not admit other items police found during a search of Mangione's backpack when he was arrested at a McDonald's restaurant in Pennsylvania a short time after the shooting. Mangione prior to Thompson's death reportedly expressed frustration about the U.S. healthcare industry.

Carro said that these items were seized during an "improper warrantless search" and included a loaded magazine, a passport, computer chip and a wallet. 

The other items, which includes a silencer, were found during a subsequent search of the backpack at Altoona police headquarters, which the judge ruled was a valid search.