The 26-year-old man accused of murdering a UnitedHealth executive in New York intends to fight his extradition to the city from Pennsylvania, where he was arrested, his defence lawyer has told a judge.
The suspect, Luigi Mangione, was also denied bail for the second time.
Mr Mangione - dressed in an orange jumpsuit - shouted and struggled with officers as he was led from a vehicle into the courtroom.
His refusal to waive extradition triggers a formal process that could last weeks, though he is unlikely to succeed in preventing his eventual transfer, according to legal experts.
The charges include possession of an unlicensed firearm, forgery and providing false identification to police.
In New York, he was charged with the murder of Brian Thompson, bringing to an end a tense manhunt.
Mr Mangione shouted something that was partly unintelligible as he arrived at the court building, but referred to an "insult to the intelligence of the American people".
Investigators are trying to retrace his movements in Pennsylvania over the past few days, as well as whether he was helped by an accomplice either before or after the shooting outside a Manhattan hotel.
Mr Mangione was captured in Altoona, Pennsylvania, after he was spotted eating at a McDonald's by a customer and an employee who believed he resembled the gunman, officials said at a news conference.
When approached by two police officers inside the restaurant and asked if he had recently been in New York, he began to shake and went quiet, one of the responding officers said.
The suspect was wearing a mask and sitting alone with a laptop and backpack.
A search of the backpack at the police station turned up a black "ghost gun" - a firearm assembled from parts, making it untraceable - loaded with a magazine and a silencer.
Pennsylvania authorities said the weapon, as well as clothing and a mask, were similar to those used by the suspect
Mr Mangione was arraigned at Blair County courthouse in Altoona last night, where gun and forgery charges were put to him.
The judge asked him if he understood the charges and he said he did. No plea was entered.
Prosecutors in New York brought a murder charge, along with four related gun charges, against the suspect, according to court records.
Pennsylvania prosecutors, citing false IDs and a large sum of cash that were found on Mr Mangione, argued he was a flight risk and asked that bail be denied, which it was.
Several electronic devices were also found with the suspect and are being examined by police.
Officers in Pennsylvania said they were working to determine if Mr Mangione had any accomplices and if he intended to kill anyone else.
They said he had been in the state for several days and were investigating exactly where he was and what he did in the state.
Mr Mangione, a Maryland native, had multiple fraudulent identifications, including a fake New Jersey ID that matched the one used by the gunman to check into a Manhattan hostel days before the shooting, officials said.
Police also found a handwritten document that speaks to "both his motivation and his mindset," New York City Police Commissioner Jessica Tisch said.
While the document did not mention specific targets, Mr Mangione harboured "ill will toward corporate America," said the NYPD's Chief of Detectives Joseph Kenny.
Mr Mangione graduated from a private all-boys school in Baltimore as valedictorian in 2016 before earning dual engineering degrees in 2020 at the University of Pennsylvania, a prestigious Ivy League university, according to school records.
His last known address was in Honolulu, officials said.
What we know about UnitedHealth CEO murder suspect Luigi Mangione
Police said that Mr Thompson, 50, appeared to be deliberately targeted outside a Manhattan hotel last Wednesday and are investigating whether others also may have been at risk.
The words "deny," "defend" and "depose" were carved into shell casings found at the scene, several news outlets have reported.
The words evoke the title of a book critical of the insurance industry published in 2010 titled 'Delay, Deny ,Defend: Why Insurance Companies Don't Pay Claims and What You Can Do About It'.
A Facebook profile that appears to belong to Mr Mangione identified him as a native of Towson, Maryland, and a former student at the University of Pennsylvania.
Photos appear to show him at Stanford University wearing Stanford-branded clothing.
Mr Mangione suffered from chronic back pain that limited his daily life, according to several news accounts.
His profile on X shows a background image of an x-ray with what appears to be screws and plates inserted in a lower back.
His family released a statement saying they knew only what had been reported in the media.
"Our family is shocked and devastated by Luigi's arrest," the family said in a statement posted to the X account of Maryland lawmaker Nino Mangione.
"We offer our prayers to the family of Brian Thompson and we ask people to pray for all involved."
Mr Thompson, a father of two, had been CEO of UnitedHealth Group's insurance unit since April 2021, part of a 20-year career with the company.
He had been in New York to attend the company's annual investor conference.
