Luigi Mangione, the man accused of fatally gunning down health insurance executive Brian Thompson on a Manhattan street, pleaded not guilty on Monday to New York state murder charges that brand him a terrorist.

Mangione, 26, was escorted into Judge Gregory Carro's 13th-floor courtroom in the New York state criminal courthouse in with a court officer on each arm, and a procession of a half dozen officers following him. He was in handcuffs and shackles, and wore a burgundy sweater over a white-collared shirt.

Mangione leaned into a microphone and said "not guilty" when Carro asked how he pleaded to the 11-count indictment charging him with murder as an act of terrorism and weapons offenses.

If convicted, he faces a maximum sentence of life in prison without the possibility of parole.

Thompson, the CEO of UnitedHealth Group's insurance unit UnitedHealthcare, was shot dead on Dec 4 outside a hotel in midtown Manhattan where the company was gathering for an investor conference.

The brazen killing and ensuing five-day manhunt captivated Americans. While public officials have condemned the killing, some Americans who decry the steep costs of healthcare and insurance companies' power to deny paying for some medical treatments have feted Mangione as a folk hero.

Mangione was arrested at a McDonald's restaurant in Altoona, Pennsylvania, on Dec 9. After deciding last week not to fight extradition, he was transferred to New York, where he was led off a helicopter in Lower Manhattan by a large phalanx of police officers and New York City Mayor Eric Adams.

That spectacle and other statements by public officials suggest Mangione may not be able to get a fair trial, his lawyer Karen Friedman Agnifilo said at Monday's hearing.

"They are treating him like he is some sort of political fodder, some sort of spectacle," Agnifilo said. "He is not a symbol, he is someone who is afforded a right to a fair trial."

Several dozen people gathered outside the courthouse in freezing temperatures to express support for Mangione and anger at healthcare companies.

One person held a sign with the words "DENY, DEFEND, DEPOSE", a phrase that echoes tactics some accuse insurers of using to avoid paying out claims. Authorities say the words "deny", "delay", and "depose" were found written on shell casings at the crime scene.

Kara Hay, a 42-year-old schoolteacher, said she believed it was wrong for Mangione to be charged with terrorism.

"Shooting one CEO does not make him a terrorist, and I do not feel terrorized," said Hay, who held a sign reading "innocent until proven guilty".

After the 30-minute hearing, officers once again shackled Mangione and led him out of the courtroom. He is being held at the Metropolitan Detention Center, a federal lockup in Brooklyn.

Carro set Mangione's next court appearance for Feb 21.

Reuters