ALTOONA, Pennsylvania (Reuters) -New York prosecutors filed a murder charge against the suspect in the killing of a UnitedHealth executive, a brazen shooting that set off a tense five-day manhunt that culminated in his capture in Pennsylvania earlier on Monday.

The suspected killer, identified as Luigi Mangione, 26, 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 McDonald's and asked if he had recently been in New York, Mangione began to shake and went quiet, one of the responding officers said at a press conference. He had been 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 killer.

Mangione was led into the Blair County courthouse in Altoona for his arraignment on Monday night, where gun and forgery charges were read against him. The judge asked Mangione if he understood the charges against him, and he said he did. No plea was entered.

Prosecutors in New York brought a murder charge, along with four related gun charges, against Mangione, according to court records.

Pennsylvania prosecutors, citing false IDs and a large sum of cash that were found on 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 they were being examined by police.

Officers in Pennsylvania said at a press conference that they were working to determine if Mangione had any accomplices and if he intended to kill anyone else. They said he had been in Pennsylvania for several days and were investigating exactly where he was and what he did in the state.

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 earlier on Monday.

While the document did not mention specific targets, Mangione harbored "ill will toward corporate America," said Joseph Kenny, the NYPD's chief of detectives.

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.

"Our family is shocked and devastated by Luigi's arrest," the Mangione family said in a statement posted on Maryland politician Nino Mangione's site on X. They said they could not comment further as they "only know what we have read in the media," and they offered their prayers to Thompson's family.

Thompson, 50, was gunned down outside a Manhattan hotel early on Wednesday morning by a masked man who appeared to wait for his arrival before shooting the executive from behind.

The suspect ran from the scene and then rode a bike into Central Park. Surveillance video captured him exiting the park and taking a taxi to a bus station in northern Manhattan, where police believe he used a bus to flee the city.

DENY DEFEND DEPOSE

Police said Thompson appeared to be deliberately targeted and were 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 Mangione identified him as a native of Towson, Maryland, and a former student at the University of Pennsylvania. Photos appear to show Mangione at Stanford University wearing Stanford-branded clothing.

An X account that appears owned by Mangione says he lives in Honolulu, Hawaii.

Thompson's murder unleashed a wave of frustration from Americans who have seen their health insurance claims or care denied, faced unexpected costs or paid more for premiums and medical care - all trends that are rising, according to recent data.

Pennsylvania Governor Josh Shapiro, speaking at a press conference with prosecutors and police in Altoona, said he understood the frustrations that some Americans, angered by health insurance companies and their refusal to pay for some treatments, had expressed online since Thompson's killing. But he rejected the glorification of the suspect in some circles online.

"In America we do not kill people in cold blood to resolve policy differences or express a viewpoint," Shapiro said.

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.

"Our hope is that today's apprehension brings some relief to Brian's family, friends, colleagues and the many others affected by this unspeakable tragedy," a spokesperson for UnitedHealth said.