Earlier on Monday, Mr. Mangione was detained at a McDonald’s in Altoona, Pa., by police officers who were responding to a tip from an employee. He was sitting alone with a laptop and backpack and wearing a medical mask, according to the complaint. One officer asked him to pull down the mask and immediately recognized him as the person being sought.

When asked if he had been to New York recently, “the male became quiet and started to shake,” according to the complaint.

He gave them a fake ID, and when the officers told him that he could be arrested for lying about his identity, he gave his true name. Asked why he had lied, he said, “I clearly shouldn’t have,” the complaint said.

The officers took him to the Altoona police station and searched his backpack, where they found a gun and silencer, both apparently made with a 3-D printer, according to the complaint. The gun’s magazine held six bullets, and the bag held a loose hollow-point round.

Before he was charged in New York, he was arraigned in Blair County, Pa., where he was charged with five crimes, including carrying a gun without a license, forgery, falsely identifying himself to the authorities and possessing “instruments of crime,” according to the criminal complaint. He appeared in court shortly after 6 p.m. in shackles for a preliminary arraignment, where he was denied bond, and, according to Gov. Josh Shapiro, will most likely be transferred to a state correctional facility this evening.

The arraignment came about nine hours after an employee at the McDonald’s spotted Mr. Mangione, recognizing him from some of the steady stream of photos released by the police in New York, and called the authorities. “He was sitting there eating,” Joseph Kenny, the New York Police Department’s chief of detectives, said at a news briefing in the early afternoon.

The fake ID that Mr. Mangione showed the police was the same one that the man believed to be the gunman presented when he checked into a hostel on the Upper West Side of Manhattan on Nov. 24, a senior law enforcement official said.

Mr. Mangione was also carrying a handwritten manifesto that criticized health care companies for putting profits above care, according to two law enforcement officials.

Here’s what else to know:

• The manifesto: Jessica Tisch, the commissioner of the New York Police Department, said the handwritten document spoke to Mr. Mangione’s “motivation and mind-set.” A senior law enforcement official who saw the document quoted it as saying, “These parasites had it coming” and “I do apologize for any strife and trauma, but it had to be done.” The manifesto mentions UnitedHealthcare by name, noting the size of the company and how much money it makes, and also broadly condemns health-care companies for placing profits over care, the official said.

• Mangione’s background: He grew up in Maryland and attended high school at the Gilman School in Baltimore, where he was an athlete and the valedictorian of his graduating class in 2016. His social media accounts and assorted other websites have offered a glimpse into his interests, including a background in the technology and video games industry and curiosity about self-improvement, clean eating and critiques of contemporary technology.

• Crucial photos: The New York Police Department began releasing images of a suspect after the fatal shooting of Brian Thompson, 50, the UnitedHealthcare chief executive, last Wednesday. One photo — crucially — showed his entire face. Seeing that image, the police said, allowed the McDonald’s employee in Altoona to spot Mr. Mangione and call the local authorities.