NEW YORK — The man accused of killing UnitedHealthcare’s CEO has been charged with murder as an act of terrorism, prosecutors said Tuesday as they worked to bring him to a New York court from from a Pennsylvania jail.

Luigi Mangione already was charged with murder in the Dec. 4 killing of Brian Thompson, but the terror allegation is new.

Under New York law, such a charge can be brought when an alleged crime is “intended to intimidate or coerce a civilian population, influence the policies of a unit of government by intimidation or coercion and affect the conduct of a unit of government by murder, assassination or kidnapping.”

Mangione’s New York lawyer has not commented on the case.

Thompson, 50, was shot dead as he walked to a Manhattan hotel where Minnesota-based UnitedHealthcare — the United States’ biggest medical insurer — was holding an investor conference.

After days of intense police searches and publicity, Mangione was arrested on Dec. 9 after being spotted in a McDonald’s in Altoona, Pennsylvania. New York police officials have said Mangione was carrying the gun used to kill Thompson, a passport and various fake IDs, including one that the suspected shooter presented to check into a New York hostel.

The 26-year-old was charged with Pennsylvania gun and forgery offenses and locked up there without bail. His Pennsylvania lawyer has questioned the evidence for the forgery charge and the legal grounding for the gun charge. The attorney also has said Mangione would fight extradition to New York.

The indictment could help move along procedural steps toward extraditing the suspect.

Hours after his arrest, the Manhattan district attorney’s office filed paperwork charging him with murder and other offenses. The indictment builds on that paperwork.

Investigators’ working theory is that Mangione, an Ivy League computer science grad from a prominent Maryland family, was propelled by anger at the U.S. health care system. A law enforcement bulletin obtained by The Associated Press week said that when arrested, he was carrying a handwritten letter that called health insurance companies “parasitic” and complained about corporate greed.

Mangione repeatedly posted on social media about how spinal surgery last year had eased his chronic back pain, encouraging people with similar conditions to speak up for themselves if told they just had to live with it.

In a Reddit post in late April, he advised someone with a back problem to seek additional opinions from surgeons and, if necessary, say the pain made it impossible to work.

“We live in a capitalist society,” Mangione wrote. “I’ve found that the medical industry responds to these key words far more urgently than you describing unbearable pain and how it’s impacting your quality of life.”

He was never a UnitedHealthcare client, according to the insurer.

Mangione apparently cut himself off from his family and close friends in recent months. His family reported him missing to San Francisco authorities in November.

Thompson, who grew up on a farm in small-town Iowa, was trained as an accountant. A married father of two high-schoolers, he had worked at the giant UnitedHealth Group for 20 years and became CEO of its insurance arm in 2021.

His killing kindled a fiery outpouring of resentment toward U.S. health insurance companies, as Americans swapped stories online and elsewhere of being denied coverage, left in limbo as doctors and insurers disagreed, and stuck with sizeable bills.

The shooting also rattled C-suites, as “wanted” posters with other health care executives’ names and faces appeared on New York streets and an outpouring of online vitriol prompted police to warn that there could be an “elevated threat.”