Murder of Brian Thompson
Murder of Brian ThompsonNYPD

The man accused of fatally shooting the CEO of UnitedHealthcare in New York pleaded not guilty Monday to state charges, including "terrorist" murder, AFP reported.

Luigi Mangione, 26, appeared in a Manhattan courtroom wearing a white shirt and burgundy sweatshirt, his hands shackled as he stood flanked by police officers.

The hearing follows Mangione's earlier court appearance last week to face federal charges, including murder, after his dramatic extradition from Pennsylvania. He was arrested at a McDonald's restaurant in Altoona after a multi-day manhunt.

Mangione faces charges in both state and federal courts for the December 4 killing of UnitedHealthcare CEO Brian Thompson.

If convicted in the state case, Mangione faces life in prison without parole. In the federal case, he could potentially face the death penalty.

Mangione’s attorney, Karen Friedman Agnifilo, has expressed concerns about the simultaneous state and federal proceedings, calling the situation "highly unusual."

Mangione was arrested on December 9 after McDonald's staff in Pennsylvania tipped off authorities. Prosecutors allege he had traveled by bus from Atlanta to New York about 10 days before the shooting, checked into a Manhattan hostel with false identification, and conducted surveillance near Thompson’s hotel and conference venue.

On December 4, Mangione allegedly followed Thompson, approached him from behind, and fired several shots using a pistol equipped with a silencer before fleeing on a bicycle.

Authorities suggest a "life-changing, life-altering" back injury may have motivated Mangione, though there is no evidence he was ever a UnitedHealthcare client.

When arrested, Mangione was found with a three-page handwritten text criticizing the US healthcare system, according to officials.