Luigi Mangione, the man accused of fatally shooting United Healthcare CEO Brian Thompson in Manhattan a year ago this week, appeared in court on Monday as his lawyers challenge the admissibility of key evidence in his case.
Mr Mangione, 27, has pleaded not guilty to both state and federal murder charges, which carry the possibility of the death penalty.
The pre-trial hearing could last several days, as defense attorneys are expected to call a host of witnesses, including those from Pennsylvania, where he was arrested at a McDonald's.
In September, a judge threw out state terrorism-related murder charges against Mr Mangione, arguing prosecutors had failed to establish evidence to justify them.
Mr Mangione's legal team is now hoping to convince a judge to exclude evidence including a gun and a notebook in which prosecutors say he set out a motive.
The defendant was arrested days after he allegedly shot Mr Thompson, a father of two, as he was walking into an investors' conference on a busy Manhattan street on 4 December 2024.
A date for either of his trials has not yet been set.
Walking into court on Monday, Mr Mangione wore a grey suit and shirt, and court employees removed his hand restraints before he sat, as his lawyers requested.
This week's hearing focuses on whether prosecutors illegally obtained evidence from Mr Mangione when they arrested him in Altoona, Pennsylvania, and whether it should be excluded as a result.
Defense attorneys are seeking to suppress some of Mr Mangione's statements made to police after being arrested - including allegedly giving them a false name - arguing he did so before police read him his rights.
His attorneys also hope to exclude a 9mm handgun said to match the one used in the killing, as well as writings found in Mr Mangione's backpack.
Prosecutors have alleged that Mr Mangione, the scion of a prominent Maryland family who graduated from an Ivy League university, wrote in his notebook about the deadly, greed fueled health insurance cartel.
Defense lawyers argue that because his backpack was searched without a warrant, the items found in it should be excluded.
Eliminating those two critical pieces of evidence would be a significant victory for Mr Mangione's legal team, but a defense attorney noted that the chances of this happening are virtually non-existent due to various exceptions to constitutional search rules.
Prosecutors claim to have other key evidence against the defendant, including DNA or fingerprints from items discarded near the crime scene.
Mr Mangione's attorneys are likely aware that obtaining evidence exclusion is a long shot but hope to glean useful witness insights during these hearings for the future trial.
Mr Mangione's legal team has also been trying to prevent the federal government from seeking the death penalty, claiming high-ranking officials have prejudiced his case through political motivations.
