Luigi Mangione is in custody in Altoona, Pennsylvania, as a person of interest in connection with the brazen Midtown Manhattan murder of UnitedHealthcare CEO Brian Thompson last week, according to authorities.

Mangione, a 26-year-old from Maryland, has been arrested by Altoona police on unrelated gun charges, according to authorities.

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

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

"He matches the description of the person we are looking for," Adams said.

Mangione had a ghost gun capable of firing a 9 mm round and a suppressor, police said. The gun and suppressor were "consistent with the weapon used in the murder," NYPD Commissioner Jessica Tisch said. The gun "may have been made on a 3D printer," police said.

Mangione also had a three-page handwritten document "that speaks to his motivation and mindset," Tisch said.

"It does seem that he had some ill will toward corporate America," police said.

Authorities are going through his writings more thoroughly to understand his motive.

Mangione also had multiple fake IDs with him, including a fake New Jersey ID matching the ID the suspect used to check into a hostel in New York City before the shooting, Tisch said.

Police also recovered clothes, including a mask, "consistent with those worn by our wanted individual," Tisch said.

Police said it appears Mangione acted alone and they did not have his name before now.

Authorities said they're working to trace his movements from New York City to Pennsylvania.

A UnitedHealth Group spokesperson said in a statement Monday, "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. We thank law enforcement and will continue to work with them on this investigation."

Mangione attended the University of Pennsylvania, where he majored in computer science and received a bachelor's degree and a master's degree in engineering, according to the university.

On Wednesday morning, the masked gunman shot Thompson at point-blank range outside the New York Hilton Midtown, where Thompson's company was holding an investors conference.

Tisch described the attack as "brazen" and "targeted."

New video obtained by ABC News shows the killer waiting for Thompson moments before the shooting.

The video shows others pass by, and then, when the masked gunman sees Thompson, he runs across the street and opens fire. The video, which has not previously been seen publicly, appears to support the police narrative that the shooter targeted Thompson because he loitered while others wandered by.

Right after the shooting, the suspect fled by bike through Central Park to the Upper West Side. He then took a taxi to the Port Authority bus facility at 178th Street and boarded a bus out of New York City, according to police.

An "enormous amount of forensic evidence" has been recovered, as well as "hundreds and hundreds and hundreds of hours" of video, police said Monday.

On Sunday, members of the New York Police Department's dive team searched underwater in Central Park near the Bethesda Fountain. Nothing was found, police said.

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.