• Luigi Mangione has been indicted in New York on a first-degree murder charge.
• Prosecutors say Mangione killed UnitedHealthcare CEO Brian Thompson "in furtherance of terrorism."
• Mangione's mother said killing Thompson was "something that she could see him doing," police said.

A Manhattan grand jury indicted Luigi Mangione on charges of first-degree murder, with prosecutors alleging he killed UnitedHealthcare CEO Brian Thompson "in furtherance of terrorism."

Prosecutors have also accused Mangione of second-degree murder, as well as a slew of counts related to the possession of an illegal "ghost gun" made from 3D-printed parts.

Following a five-day manhunt, Mangione was arrested last week at a restaurant in Altoona, Pennsylvania, on gun and false ID charges.

Police say he killed Thompson outside a midtown Manhattan hotel on December 4.

"This killing was intended to invoke terror," Manhattan District Attorney Alvin Bragg said at a press conference Tuesday afternoon, calling it a"brazen, targeted and premeditated shooting."

Prosecutors offered a detailed look at Mangione's movements Tuesday. They say he stayed at an Upper West Side hostel for more than a week, using a fake New Jersey ID, before carrying out the killing.

According to prosecutors, two of the shell casings for the bullets that killed Thompson had the words "DENY" and "DEPOSE" written on them. The word "DELAY" was written on a bullet found at the scene.

An arrest warrant previously obtained by Business Insider indicated that Mangione would be charged with second-degree murder along with four other charges related to illegal weapon possession. The first-degree murder charge reflects a more severe charge.

If Mangione, 26, is convicted of the first-degree murder charge, he could spend the rest of his life in prison without parole. The charge, with the intent to commit terrorism, refers to a killing that is "intended to intimidate or coerce a civilian population" or "influence the policies of a unit of government by intimidation or coercion," according to the indictment.

Mangione has not yet entered a plea for any of the charges against him.

Even the minimum required sentence for first-degree murder, 25 to life, would mean Mangione would not see a parole officer until age 51.

The top charge could become a bargaining chip for Bragg, former Manhattan prosecutor Michael Bachner, who is now in private practice, told BI.

"Given the risk now of a maximum sentence of life without the possibility parole, that top terrorism count may induce the defendant to enter a plea, if one is offered," he said.

Jessica Tisch, the New York City police commissioner, lambasted the "ghoulish" online discourse valorizing Mangione for killing Thompson.

"Let me say this plainly — there is no heroism in what Luigi Mangione did," she said.

A Pennsylvania-based attorney for Mangione, an Ivy League graduate, has contested Mangione's extradition to Manhattan. At Tuesday's press conference, Bragg said he believed Mangione may change tack court proceedings Thursday and stop fighting extradition.

Over the weekend, Mangione hired Karen Friedman Agnifilo, an experienced New York-based criminal defense attorney who is married to and shares a law firm with Marc Agnifilo. Marc Agnifilo is representing Sean "Diddy" Combs in his criminal sex-trafficking case.

In an interview with CNN prior to taking on Mangione as a client, Friedman Agnifilio said the evidence was "overwhelming" that Mangione killed Thompson.

"It looks like to me there might be a 'not guilty by reason of insanity' defense that they're going to be thinking about because the evidence is going to be so overwhelming that he did what he did," she said.

Mangione left a robust online trail that went cold about six months before Thompson's killing. His mother filed a missing persons report in San Francisco in November, saying he had disappeared.

At Tuesday's press conference, Joe Kenny, the New York Police Department's chief of detectives, said the FBI contacted Mangione's mother on December 7, following a tip.

"She didn't indicate that it was her son in the photograph, but she said it might be something that she could see him doing," Kenny said.