Luigi Mangione, the 26-year-old man accused of fatally shooting  United Healthcare CEO Brian Thompson, has pleaded not guilty to New York state charges that allege he committed an “act of terrorism”.

The plea made in a Manhattan court on Monday came days after federal prosecutors lodged their own charges against Mangione in connection with the December 4 killing of Thompson outside a Midtown Manhattan hotel.

Mangione was arrested in Pennsylvania on December 9 and was extradited last week to New York. He appeared in court on Monday in handcuffs and wore a burgundy sweater over a white collared shirt.

Leaning into a microphone, he said “not guilty” when asked how he pleaded to the 11-count indictment, which includes three murder charges, including murder as an “act of terrorism”.

He faces life in prison if convicted of the state charges but could face the death penalty if convicted on the federal charges.

Last week, Mangione, who is a graduate of the prestigious University of Pennsylvania and hails from an influential Maryland family, appeared in federal court in New York for the first time.

He was not asked to enter a plea on the federal charges. They include one count of using a firearm to commit murder, one count of interstate stalking resulting in death and one count of stalking through use of interstate facilities resulting in death.

‘Deny, defend, depose’

Thompson’s killing has drawn renewed scrutiny of the US healthcare system, in which high costs often leave patients vulnerable to the decisions of insurance companies.

UnitedHealthcare is the largest health insurer in the country.

Long simmering anger towards the industry has been apparent in the wake of the attack with some hailing Mangione as a folk hero. A mention of Mangione during the Saturday Night Live comedy programme on Saturday prompted cheers from the crowd.

Even many medical professionals and patients who have condemned the violence have taken to social media in recent days to share stories of insurance companies denying claims.

About two dozen members of the public were in attendance at Mangione’s arraignment, and a small group of supporters gathered outside.

One person held a sign that read “Deny, Defend, Depose”, a reference to the words found etched on the bullet casings at the scene of Thompson’s killing. The words are often used by critics to describe how health insurance companies dodge paying out claims, leading to care being denied or patients forced to pay for large bills out of their own pocket.

According to the federal criminal complaint, the police who arrested Mangione found a notebook that contained several handwritten pages that “express hostility towards the health insurance industry and wealthy executives in particular”.

A notebook entry dated October 22 allegedly described an intent to “wack” the chief executive of an insurance company at its investor conference.