A man has been charged with murder over last week's fatal shooting of UnitedHealthcare CEO Brian Thompson in New York City.

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.

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.

Luigi Mangione was arrested at a McDonald's

Luigi Mangione was charged for the murder of UnitedHealth executive Brian Thompson

Officials at the Blair County Courthouse attend a press conference following Luigi Mangione's arrest

Court records show prosecutors in New York brought a murder charge, along with four related gun charges, against Mangione.

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 at the restaurant 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.

A person holds a sign while standing on the roadside near the McDonald's restaurant where Mangione was arrested

Luigi Mangione, 26, a suspect in the New York City killing of UnitedHealth executive Brian Thompson

Pennsylvania authorities said the weapon, as well as clothing and a mask, were similar to those used by the killer.

Police also found a handwritten document that speaks to "both his motivation and his mindset," New York City Police Commissioner Jessica Tisch told a press conference.

Officers said Mangione was born and raised in Maryland, went to college in Pennsylvania and is thought to have had "ill will toward corporate America" based on a document found on him, according to Joseph Kenny, chief of detectives for the New York Police.

Mangione has ties to San Francisco, lived in Honolulu until recently and is believed to have acted on his own, Kenny said. He has no known criminal record in New York, Kenny said.