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.

The new details emerged as Mr. Mangione arrived at the courthouse in Blair County, Pa., shortly after 6 p.m. in shackles for a preliminary arraignment. 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,” the complaint said. 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.

Reporting was contributed by Maria Cramer , Corey Kilgannon , Mike Isaac and Brian Conway .

The man, whom the police identified as Luigi Mangione, 26, of Maryland, was carrying a gun, a silencer and some kind of manifesto, the police said.

Chief Kenny said that it was hard to credit the break in the case to any one moment or piece of evidence, but that if he had to, “it would be the release of that photograph to the media.”

For experts, the case was a reminder of how — even as facial recognition technology grows more sophisticated — distributing photos and relying on the public to recognize a face can still play a critical role in investigations.

Sean Patrick Griffin, a former Philadelphia police officer and a criminal justice professor at The Citadel, a military college in South Carolina, said this was not a typical case. “That photo has been seen more times than in your average homicide,” said Mr. Griffin, who added that the photos also showed enough of the man’s face to play a useful role.

In the photo that appears to have led to Mr. Mangione’s arrest, the suspect has distinct facial features: dark eyes and eyebrows, high cheekbones and a broad smile that curls at the corners. “Not just dark, but prominent eyebrows,” said Mr. Griffin, who said that such a recognizable trait was not ideal for someone seeking to get away with a high-profile crime.

Robert Baer, a former C.I.A. officer and the author of several books, including “The Perfect Kill: 21 Laws for Assassins,” said he was surprised only that it had taken so long for the police to find someone. “Once they had that guy’s picture, when he pulls his mask down, it was a given he would be arrested,” he said.

Like other experts, Mr. Baer mentioned that a professional hit man would have been more careful about exposing his face on camera.

The arrest, on gun charges and for questioning in connection with the shooting, came five days after Mr. Thompson was killed outside a Hilton hotel in Midtown. Within hours, the police released grainy images of a man wearing a backpack, his arms extended as he fired his gun, and, later, riding a bicycle as he fled.

More images of the suspect were soon released. Two photos — captured by cameras at the hostel on the Upper West Side of Manhattan where he stayed — showed a man in a hooded jacket. His face was not covered, and in one, he was smiling.

Over the weekend, two images emerged showing a man in a slightly different get-up — a surgical mask and a black coat — taken from a taxi. In one, he is seen peering through the partition in the cab, his dark eyes and eyebrows clearly visible above his mask.

The images helped fuel broad interest in the case.

Some people drew comparisons to celebrities. There was at least one look-alike contest, in a Manhattan park. The suspect even had something like fans, because, in the words of one expert, Michael C. Farkas, “people hate the health care insurance industry.”

Mr. Farkas added that many people, however, were clearly interested in helping law enforcement solve the case.

“There’s a reason why people are still doing things that would seem strange, like printing ‘Wanted’ posters,” said Mr. Farkas, a defense lawyer who has worked as a New York City homicide prosecutor. “People actually recognize photos from hard-copy sources.”

Maria Cramer contributed reporting.

Mr. Mangione, 26, worked for a number of tech companies over the past 10 years, according to his LinkedIn profile and a former employer. He also maintained an active online presence on gaming platforms like Steam, and co-founded UPGRADE, the University of Pennsylvania’s first video game development club, when he was a student there.

Mr. Mangione’s interest in games started at a young age, when he began exploring the independent gaming community online, according to a now-deleted interview published to the University of Pennsylvania’s campus events blog, Penn Today, in 2018. He wanted to start creating games himself, and taught himself to code in high school.

“That’s why I’m a computer science major now, that’s how I got into it,” Mr. Mangione said in the 2018 interview. “I just really wanted to make games.”

The University of Pennsylvania did not immediately respond to a request for comment.

Along with a handful of friends, Mr. Mangione started his own game development company, Approar Games, in high school, according to posts on his LinkedIn profile and social media accounts. The group published at least one app, called Pivot Plane.

Later, Mr. Mangione went to work as an intern at Firaxis Games, publisher of the enormously popular computer game franchise Civilization, according to his LinkedIn profile. He worked on the fifth installment of the game and, as part of a team of 10 people, fixed more than 300 bugs in the user interface, according to the profile.

A spokesman for Take-Two Interactive, the owner of Firaxis, confirmed that Mr. Mangione was a former employee but declined to comment further.

At a news conference on Monday, Joseph Kenny, chief of detectives for the New York Police Department, described Mr. Mangione as born and raised in Maryland, with ties to San Francisco, and said he had lived in Honolulu until recently.

Mr. Mangione’s passion for games and engineering ultimately led him to pursue bachelor’s and master’s degrees in computer engineering at Penn, where he graduated in 2020, according to his LinkedIn profile. He went on to work as a data engineer at TrueCar, a digital marketplace start-up in Los Angeles that connects car buyers and sellers, according to the 2018 interview.

TrueCar confirmed that Mr. Mangione worked at the company, but said he has not been an employee since 2023.

In the interview with Penn Today, Mr. Mangione said he could never imagine a future in which he would no longer make games, and that he had created his college club to rally others to see the “benefits and pure fun” of making them.

“Passion is what we’re looking for,” he said.

He attended high school at the Gilman School in Baltimore, where he was an athlete and displayed a keen interest in developing video games. According to an interview that was published on the University of Pennsylvania’s campus events blog, Penn Today, in 2018 and that has now been deleted, Mr. Mangione taught himself to code in high school. He and a group of friends then started a game development company, Approar Games, according to posts on his LinkedIn profile and social media accounts.

He was the valedictorian of his graduating class in 2016. In a graduation speech, he described his class as “coming up with new ideas and challenging the world around it.”

He thanked parents in attendance for sending him and his classmates to the school, which he described as “far from a small financial investment.” Tuition at Gilman is currently $37,690 per year for high schoolers.

Mr. Mangione then attended the University of Pennsylvania, where he co-founded a game development club. He was a member of the Phi Kappa Psi fraternity and Eta Kappa Nu, an academic honor society for students in electrical and computer engineering, and graduated with both a bachelor’s degree and a master’s degree in engineering.

Stanford University confirmed that a Luigi Mangione worked as a head counselor in its Pre-Collegiate Studies program in 2019.

Mr. Mangione also had an internship at Firaxis Games, the publisher of the enormously popular computer game franchise Civilization. He went on to work as a data engineer at TrueCar, a digital marketplace start-up in Los Angeles that connects car buyers and sellers. TrueCar said he had not been an employee since 2023.

Mr. Mangione’s family is prosperous, thanks to real estate holdings and a chain of senior rehabilitation centers.

Chief Kenny said Mr. Mangione had lived in San Francisco and Honolulu and had no known criminal record in New York City. In fact, the only criminal activity that seems linked to Mr. Mangione is a citation for trespassing in Hawaii.

In recent months, Mr. Mangione appeared to maintain accounts on social media platforms including Facebook, X, Instagram and Goodreads, where he shared quotations, reviewed books he had read and reflected on algorithms, self-help texts and guides to touring Hawaii.

On X, Mr. Mangione frequently reposted content from a handful of well-known writers and academics, many of whom focus on self-improvement or the negative health consequences of modern consumption.

On Goodreads, a book review website, earlier this year, he gave four stars to “Industrial Society and Its Future,” better known as the Unabomber manifesto, by Ted Kaczynski, and described the writer as a “mathematics prodigy.”

“He was a violent individual — rightfully imprisoned — who maimed innocent people,” Mr. Mangione wrote in his review. “While these actions tend to be characterized as those of a crazy luddite, however, they are more accurately seen as those of an extreme political revolutionary.”

Posts on social media from before Mr. Mangione was apprehended indicate that he may have fallen out of touch with some of his circle. Former classmates said they had heard that he had been out of contact with his peers after suffering a spinal injury last year and having surgery, and that Mr. Mangione’s family had been trying to track him down for several months.

A handwritten manifesto found with Mr. Mangione on Monday 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, according to a senior law enforcement official who saw the document. The official quoted it as saying, “These parasites had it coming” and “I do apologize for any strife and trauma, but it had to be done.”

Reporting was contributed by Mike Baker , Maria Cramer , Heather Knight , Mike Isaac , Madison Malone Kircher , Joseph Bernstein , Callie Holtermann , Dani Blum and Andy Newman .

His LinkedIn profile lists two degrees, a master’s and a bachelor’s in computer science completed in four years, from the University of Pennsylvania. An interview with Mr. Mangione on a page on the university’s website that is now unavailable described him as having started a video game research and development club after reaching out to classmates via a Facebook group for students in the class of 2020. From there, according to his LinkedIn profile, he went on to work as a data engineer.

Mr. Mangione’s X account doesn’t include much that would mark him out from any other young man working in tech. He frequently reposted content from a handful of well-known figures, many of whom focus on self-improvement or the negative health consequences of modern consumption.

They include Andrew Huberman, a Stanford neuroscientist who hosts a popular health and science podcast; Tim Urban, a writer and illustrator with a wide readership in Silicon Valley whose most recent book is “What’s Our Problem: A Self-Help Book for Societies”; Tim Ferriss, an entrepreneur known for his book “The 4-Hour Workweek”; Michael Pollan, who writes about the hazards of processed foods; and Jonathan Haidt, a psychologist at New York University who has written about the dangers of smartphone use by young people. (Mr. Urban has already distanced himself from Mr. Mangione, writing on X on Monday afternoon, “Very much not the point of the book.”)

On the book review website Goodreads, Mr. Mangione appeared to track his reading habits. His selections include science fiction (“Ender’s Game”), airport bookstore standbys (“Freakonomics,” “Outliers”) and young adult classics like the “Harry Potter” and “Hunger Games” series.

In some of his reviews, Mr. Mangione linked to Google Docs where he kept more detailed notes. In one scanned handwritten document, he shared his thoughts on the popular science book “Grit: The Power of Passion and Perseverance” by Angela Duckworth.

Earlier this year, he left a four-star review for “Industrial Society and Its Future,” better known as the Unabomber manifesto, by Ted Kaczynski, whom Mr. Mangione described as a “mathematics prodigy” in his review of the work.

“It’s easy to quickly and thoughtless write this off as the manifesto of a lunatic, in order to avoid facing some of the uncomfortable problems it identifies,” Mr. Mangione wrote. “But it’s simply impossible to ignore how prescient many of his predictions about modern society turned out.”

He added: “He was a violent individual — rightfully imprisoned — who maimed innocent people. While these actions tend to be characterized as those of a crazy luddite, however, they are more accurately seen as those of an extreme political revolutionary.”

Mr. Mangione highlighted a quotation from the children’s book “The Lorax” by Dr. Seuss, which he also shared this year. (He gave the book five out of five stars.)

The selected quotation read: “Unless someone like you cares a whole awful lot, nothing is going to get better. It’s not.”

On his “wants to read” list, Mr. Mangione included a forthcoming title, “Life & the Lindy Effect” by Paul Skallas, who is known for arguing that the longer a phenomenon has been around, the better its chance of lasting far into the future.

Jessica Testa contributed reporting.

A correction was made on

Dec. 9, 2024

:

An earlier version of this story misstated Jonathan Haidt’s profession. He is a psychologist, not a sociologist.

When we learn of a mistake, we acknowledge it with a correction. If you spot an error, please let us know at nytnews@nytimes.com.Learn more

Ghost guns are sold as do-it-yourself kits and shipped in parts so that buyers can carry out the final assembly themselves.

They have been sold since the 1990s but have become popular in recent years, particularly among criminals barred from buying ordinary guns, and have been a major issue in the larger national debate over gun control.

The issue became central to President Biden’s initiative to address gun violence.

In 2022, the Bureau of Alcohol, Tobacco, Firearms and Explosives broadened its interpretation of the definition of “firearm” in the Gun Control Act of 1968. Solicitor General Elizabeth B. Prelogar wrote in the Biden administration’s emergency application that the change was needed to respond to “the urgent public safety and law enforcement crisis posed by the exponential rise of untraceable firearms.”

The regulation did not ban the sale or possession of the do-it-yourself kits, but required manufacturers and sellers to obtain licenses, mark their products with serial numbers and conduct background checks. Opponents challenged the law, saying the regulations were not authorized by the 1968 law.

After a federal court in Texas struck the law down in 2023, the Supreme Court later revived the regulations, allowing them to remain in place while a challenge moved forward. During arguments in October, a majority of the court appeared sympathetic to the Biden administration’s restrictions, with two conservatives — Chief Justice John G. Roberts Jr. and Justice Amy Coney Barrett — joining the liberal wing.

“The reason why you want a ghost gun is specifically because it’s unserialized and can’t be traced,” Ms. Prelogar said during the arguments.

In September, Mr. Biden signed an executive order to establish a task force to assess the threat posed by ghost guns.