Lawyers for Luigi Mangione asked a New York federal judge to dismiss some criminal charges, including the only count carrying the death penalty, in connection with the December assassination of UnitedHealthcare CEO Brian Thompson.

They argued that prosecutors should be barred from using Mangione’s statements to law enforcement and evidence from his backpack, which contained a gun and ammunition.

Mangione, 27, was arrested after Thompson was fatally shot as he arrived at a Manhattan hotel for an investor conference.

His attorneys claim he was not read his rights before questioning and that the backpack search lacked a warrant, NBC News has reported.

Mangione has pleaded not guilty to both state and federal charges, and authorities had pursued him across multiple states following the shooting.