Luigi Mangione has pleaded not guilty to of gunning down United States health insurance executive Brian Thompson, a day after prosecutors formally stated their intent to seek the death penalty.
Wearing a tan jail-issued T-shirt in a packed lower Manhattan courtroom on Friday, Mangione stood up as US district judge Margaret Garnett asked for his plea.
"Not guilty," he said, leaning down to speak into a microphone on the defence table.
Mangione, 26, previously over the 4 December killing of Thompson, the former CEO of UnitedHealth Group's insurance unit UnitedHealthcare.
Earlier this month, US attorney-general Pam Bondi announced the Justice Department would seek the death penalty for Mangione.
The Manhattan US attorney's office formalised its intent this week.
Protesters gathered outside court during Luigi Mangione's hearing. Source: AAP / Sarah Yenesel/EPA
Garnett gave the defence until 27 June to file a legal brief laying out their arguments as to why the government should be barred from pursuing capital punishment.
The judge set Mangione's next court date for 5 December, and said she would aim for a trial date some time next year.
The , where the company had gathered for an investor conference, and the ensuing five-day manhunt, captivated Americans.
While public officials condemned the killing, some Americans have cheered Mangione, saying he drew attention to steep US healthcare costs and the power of health insurers to refuse payment for some treatments.
Mangione is currently being held in federal lockup in Brooklyn.
