Authorities say police are questioning 26-year-old Luigi Mangione in Altoona, Pennsylvania, as a person of interest in the brazen murder of UnitedHealthcare CEO Brian Thompson in midtown Manhattan last week.

According to authorities, Mangione, of Maryland, was arrested by Altoona police on firearms charges.

Sources said he was on a Greyhound bus traveling through Altoona on Monday morning when he got off and walked into a McDonald’s, where a witness recognized him from images of the suspect distributed by police.

Mangione was sitting eating when a McDonald’s employee reported him, and “for that reason, we believe we have a strong person of interest,” New York Mayor Eric Adams said at a news conference Monday.

“He fits the description of the person we’re looking for,” Adams said.

Mangione was in possession of a handwritten document “that reflects his motivation and mindset,” said NYPD Commissioner Jessica Tisch.

“It appears that he had some dislike for the American economy,” police said.

The police are going through his writings more thoroughly to understand his motive.

According to police, Mangione also had a ghost gun that could fire a 9mm cartridge and a silencer.

He also was in possession of a fake New Jersey driver’s license, similar to the one the suspect used to check into a New York City hostel before the shooting, she said.

Tisch praised the NYPD’s “good, old-fashioned detective work” and the “power of publicity” that led to the arrest.

Police said it appeared he acted alone.

Police said they were working to trace his movements from New York City to Pennsylvania.

Police said they did not yet know his name.

Meanwhile, new video from ABC News shows the killer waiting for Thompson moments before the shooting.

The video shows others walking by, and then when the masked gunman sees Thompson, he runs across the street and opens fire.

The video, which has not been seen publicly, appears to support the police account that the gunman targeted Thompson because he was loitering while others walked by.

On Wednesday morning, the masked gunman shot Thompson at close range outside New York’s Hilton Midtown, where Thompson’s company was holding an investor conference. Tisch described the attack as “brazen” and “targeted.”

Immediately after the shooting, the suspect fled on a bicycle through Central Park to the Upper West Side. According to police, he then took a taxi to the Port Authority bus station on 178th Street and boarded a bus from there.

On Sunday, members of the New York Police Department’s dive team searched underwater in Central Park near the Bethesda Fountain.

The suspect’s backpack – with a jacket and Monopoly money inside – was found nearby in Central Park.

This is a developing story. Please check back for updates.

ABC News’ Bill Hutchinson, Jon Haworth, Ivan Pereira and David Brennan contributed to this report.