NEW YORK, Feb 21 (Reuters) -

Luigi Mangione, the man accused of fatally gunning down

health insurance executive Brian Thompson on a Manhattan street

in December, arrived in court in New York on Friday afternoon as

he faces state murder and terrorism charges.

Mangione, 26, wore a green cable knit sweater over a white

shirt. He was brought into the courtroom in leg and arm shackles

and wearing a bulletproof vest.

Mangione pleaded not guilty on December 23 to an 11-count

indictment charging him with murder as an act of terrorism and

weapons offenses.

If convicted, Mangione could face life in prison without

parole. He is now jailed in a federal lockup in Brooklyn.

Thompson, the former CEO of UnitedHealth Group's ( UNH )

insurance unit UnitedHealthcare, was shot dead on December 4

outside a Midtown Manhattan hotel, where the company was

gathering for an investor conference.

The brazen killing and ensuing five-day manhunt captivated

Americans.

While public officials condemned the killing, some Americans

who decry steep healthcare costs and insurers' power to refuse

to pay for some treatments have feted Mangione as a folk hero.

Dozens of Mangione supporters gathered outside the

courthouse on Friday and behind police barricades in the hall

outside the courtroom.

Mangione also faces a four-count federal criminal complaint

charging him with stalking and killing Thompson.

He has not yet entered a plea in that case, where he could

face the death penalty.

Avraham Moskowitz, a lawyer with experience in death penalty

cases, joined Mangione's defense team this month.

Mangione's lawyers in the state case expressed concern

during his last court appearance that he might not get a fair

trial because of the intense publicity and statements by

officials condemning him.