The suspect in the killing of UnitedHealthcare's CEO struggled with deputies and shouted Tuesday while arriving for a court appearance in Pennsylvania, a day after he was arrested at a McDonald's and charged with murder.

Luigi Nicholas Mangione emerged from a patrol car, spun toward reporters and shouted something partly unintelligible referring to an "insult to the intelligence of the American people" while deputies pushed him inside.

Prosecutors were beginning to take steps to bring Mangione back to New York to face a murder charge while new details emerged about his life and how he was captured.

The 26-year-old Ivy League graduate from a prominent Maryland real estate family was charged with murder hours after he was arrested in the Manhattan killing of Brian Thompson, who led the United States' largest medical insurance company.

At the brief hearing, defence lawyer Thomas Dickey informed the court that Mangione will not waive extradition to New York but instead wants a hearing on the issue. Mangione was denied bail after prosecutors raised concerns about public safety and a potential flight risk.

Mangione, wearing an orange prison jumpsuit, mostly stared straight ahead at the hearing, occasionally consulting papers, rocking in his chair or looking back at the gallery. At one point, he began to speak to respond to the court discussion but was quieted by his lawyer.

"You can't rush to judgment in this case or any case," Dickey said afterward. "He's presumed innocent. Let's not forget that."

New York Gov. Kathy Hochul said Tuesday night on the social media platform X that she will sign a request for a governor's warrant "to ensure the suspect in the murder of Brian Thompson is held accountable in New York."

Mangione likely was motivated by his anger with what he called "parasitic" health insurance companies and a disdain for corporate greed, according to a law enforcement bulletin obtained by The Associated Press.

He wrote that the U.S. has the most expensive health-care system in the world and that profits of major corporations continue to rise while "our life expectancy" does not, the bulletin said, based on a review of his hand-written notes and social media posts.

Mangione called Ted Kaczynski — known as the Unabomber — a "political revolutionary" and may have found inspiration from the man who carried out a series of bombings while railing against modern society and technology, according to the police bulletin.

Mangione remained jailed in Pennsylvania, where he was initially charged with possession of an unlicensed firearm, forgery and providing false identification to police. Manhattan prosecutors have obtained an arrest warrant, a step that could help expedite his extradition from Pennsylvania.

End to five-day manhunt

Mangione was arrested in Altoona, Pa., about 370 kilometres west of New York City, after a McDonald's customer recognized him and notified an employee, authorities said.

Officers found him sitting at a back table, wearing a blue medical mask and looking at a laptop, according to a Pennsylvania police criminal complaint.

He initially gave them a fake ID, but when an officer asked Mangione whether he'd been to New York recently, he "became quiet and started to shake," the complaint says.

When he pulled his mask down at officers' request, "we knew that was our guy," said police officer Tyler Frye.

Images of Mangione released Tuesday by Pennsylvania State Police showed him pulling down his mask in the corner of the McDonald's while holding what appeared to be hash browns and wearing a winter jacket and beanie. In another photo from a holding cell, he stood unsmiling with rumpled hair.

New York Police Commissioner Jessica Tisch said Mangione was carrying a gun like the one used to kill Thompson and the same fake ID the shooter had used to check into a New York hostel, along with a passport and other fraudulent IDs.

NYPD Chief of Detectives Joseph Kenny said Mangione also had a three-page, handwritten document that shows "some ill will toward corporate America."

A law enforcement official — who wasn't authorized to discuss the investigation publicly and spoke with The Associated Press on condition of anonymity — said the document included a line in which Mangione claimed to have acted alone.

"To the Feds, I'll keep this short, because I do respect what you do for our country. To save you a lengthy investigation, I state plainly that I wasn't working with anyone," the document said, according to the official.

It also had a line that said, "I do apologize for any strife or traumas but it had to be done. Frankly, these parasites simply had it coming."

Pennsylvania prosecutor Peter Weeks said in court that Mangione was found with a passport and $10,000 in cash, $2,000 of it in foreign currency. Mangione disputed the amount.

Thompson, 50, was killed Wednesday as he walked alone to a Manhattan hotel for an investor conference.

WATCH | Mangione will fight extradition to New York: 

UnitedHealthcare CEO murder suspect Luigi Mangione denied bail

Luigi Mangione, the suspect charged with the murder of UnitedHealthcare CEO Brian Thompson, was denied bail by a judge in Pennsylvania Tuesday.

Police quickly came to see the shooting as a targeted attack by a gunman who appeared to wait for Thompson, came up behind him and fired a 9-mm pistol.

Investigators have said "delay," "deny" and "depose" were written on ammunition found near Thompson's body. The words mimic "delay, deny, defend," a phrase used to criticize the insurance industry.

From surveillance video, New York investigators determined the shooter quickly fled the city, likely by bus.

From wealth and success to murder suspect

A grandson of a wealthy, self-made real estate developer and philanthropist, Mangione is a cousin of a current Maryland state legislator.

Valedictorian at his elite Baltimore prep school, he went on to earn undergraduate and graduate degrees in computer science in 2020 from the University of Pennsylvania, a spokesperson said.

"Our family is shocked and devastated by Luigi's arrest," Mangione's family said in a statement posted on social media late Monday by his cousin, Maryland Del. Nino Mangione.

"We offer our prayers to the family of Brian Thompson and we ask people to pray for all involved."

From January to June 2022, Luigi Mangione lived at Surfbreak, a "co-living" space at the edge of the touristy Waikiki neighbourhood in Honolulu.

Like other residents of the shared penthouse catering to remote workers, Mangione underwent a background check, said Josiah Ryan, a spokesperson for owner and founder R.J. Martin.

"Luigi was just widely considered to be a great guy. There were no complaints," Ryan said.

"There was no sign that might point to these alleged crimes they're saying he committed."

At Surfbreak, Martin learned Mangione had severe back pain from childhood that interfered with many aspects of his life, from surfing to romance, Ryan said.

Mangione left Surfbreak to get surgery on the mainland, Ryan said, then later returned to Honolulu and rented an apartment.

Martin stopped hearing from Mangione six months to a year ago.