Luigi Mangione—the 26-year-old identified by authorities as a “strong person of interest” in the fatal shooting of UnitedHealthcare CEO Brian Thompson last week—was formally charged with murder in New York late Monday after being arrested in Pennsylvania and found with a three-page manifesto that gave insight into the alleged killing.

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Thompson, 50, was the CEO of the health insurance division of the $550 billion UnitedHealth Group and was in New York City on Wednesday for UnitedHealth Group’s investor meeting. He was shot from behind just before 7 a.m. on Dec. 4 outside of the New York Hilton Midtown—where the meeting was being held—and was hit in the back and right calf, after which the suspect fled the area on foot and on an electric bike. A Minnesota resident, Thompson had served as chief executive since April 2021 and had been with UnitedHealth Group since 2004. A video of the shooting showed the suspect walk out behind Thompson—who did not have a security detail—before firing multiple times. Prior to Mangione’s arrest, police said they believed the shooting was “a brazen targeted attack” and searched New York City before saying they believed the suspect had left the city on a bus. Thompson’s wife, Paulette Thompson, told NBC News “there had been some threats,” but didn’t provide details on what the threats were. Thompson had two sons, one who just graduated from high school and one still in high school. Police had been searching for the gunman by utilizing diving teams in Central Park, flying helicopters, searching through security cameras in the area, maintaining drones and using dogs. They released several photos of the suspected shooter since Wednesday.

New York City Police Commissioner Jessica Tisch said Mangione was recognized in a McDonald’s in Altoona, Pennsylvania, and was reported to local police, who then found he had “multiple fraudulent IDs,” a U.S. passport, a firearm and suppressor similar to what was used in the murder and a “handwritten document that speaks to both his motivation and mindset.” Officers reportedly asked Mangione if he was in New York recently, which resulted in him becoming quiet and shaking, according to a description of his arrest. Though his face was largely covered in most pictures law enforcement released, officials credited the images that were circulating of Mangion for him eventually being spotted and taken into custody.

In addition to the murder and gun charges in New York state, Mangione was initially charged in Pennsylvania with forgery, carrying firearms without a license, tampering with records or identification, possessing instruments of a crime and providing false identification to law enforcement. He was ordered to be held without bail in his arraignment Monday night, and is being held in a single cell at the “maximum custody level,” Maria Bivens, press secretary for the Pennsylvania Department of Corrections, told CNN.

It’s unclear when Mangione will be extradited to New York. He was arraigned on the Pennsylvania charges Monday night, and a preliminary hearing in that state is scheduled for Dec. 23. The court docket says he requested a public defender.

A description of Mangione’s arrest notes officers found a 3D-printed pistol and 3D-printed silencer in his backpack. The pistol was loaded with a Glock magazine containing six nine-millimeter full metal jacket rounds. A loose nine-millimeter hollow point round was also found in the backpack. Authorities have said the gun and silencer are consistent with the firearm used in the shooting of Thompson.

Police have not named a formal motive in the killing of Thompson. Officers found three 9mm rounds at the scene and bullet casings had the words “deny,” “defend” and “depose” on them, which echo a phrase commonly used to criticize tactics insurance companies use to reject claims. At Monday’s press conference, Kenny said the three-page handwritten manifesto found on Mangione when he was arrested is in the possession of the Altoona Police Department, but that “it does seem that he has some ill will toward corporate America.” Kenny also said there were no other “specific threats” to people in the document. Citing an unnamed law enforcement official, the Associated Press reported that in the document mentioned Mangione admitted to working alone, stating: “To the Feds, I’ll keep this short, because I do respect what you do for our country. To save you a lengthy investigation, I state plainly that I wasn’t working with anyone.” The note added, “I do apologize for any strife or traumas but it had to be done. Frankly, these parasites simply had it coming.”

Mangione’s mother, Kathleen Mangione, reported him missing to the San Francisco police last month. According to the San Francisco Standard, the missing person report was filed on Nov. 18 although it is unclear if Mangione was supposed to be present in the city when his mother filed the report. Although he was born and raised in Maryland, NYPD Chief of Detectives Joseph Kenny said he has “ties to San Francisco” and most recently resided in Honolulu.

Mangione graduated from the University of Pennsylvania in 2020 with bachelor's and master's degrees in computer and information science, according to social media accounts appearing to belong to him and the university’s alumni database. The Daily Pennsylvanian—Penn’s student newspaper—reported that Mangione founded the school’s Game Research and Development Environment club and that he was inducted into the Eta Kappa Nu honor society for excellence in electrical and computer engineering before graduating in 2020. A post on an Instagram account seeming to belong to him as well shows him affiliated with the fraternity Phi Kappa Psi.

In Honolulu, where police said Mangione’s last known address was, he was a member of a co-working space called Hub Coworking Hawaii, the Honolulu Star-Advertiser reported. Mangione would reportedly come and work at the location with his roommates from a nearby co-living space called Surfbreak. On its website, Surfbreak describes itself as a “co-living and co-working community for digital nomads and remote workers.” Surfbreak founder and CEO R.J. Martin expressed shock about Mangione’s arrest and told the Honolulu Civil Beat, “I loved this guy…In some ways I feel like my members are my kids.” According to the report, other residents of the co-living space described Mangione as a “natural leader” and said he helped found a book club in the community. Martin and another resident told the outlet that they had suggested the book club should read “Industrial Society and Its Future”—a book written by Unabomber Ted Kaczynski Kaczynski—as “a joke.”

A Goodreads account seeming to belong to Mangione gave the book a four-star review in January. The review written by the account—which was made private on Monday—said, “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. But it's simply impossible to ignore how prescient many of his predictions about modern society turned out.” The review also quoted another person’s take about how “violence is necessary to survive.”

Nearly all social media accounts with reported ties to Mangione on Monday had been switched to private or taken down by platforms—including the Goodreads account with his name, a YouTube account that was speculated to be his and his Facebook and Instagram accounts—with one notable exception. Mangione’s account on X, formerly known as Twitter, was briefly taken down Monday evening, but X owner Elon Musk said it was done “without his knowledge” and he was looking into it. Shortly after, the account was reinstated. Mangione’s X account—which has a cover photo featuring an apparent spinal injury—had more than 300,000 followers as of Tuesday morning.

Mangione’s friends in Hawaii told various news outlets that he was suffering from a serious back problem that caused him significant pain. Mangione left Hawaii to get back surgery last year and then returned to Honolulu to rent an apartment. Surfbreak’s Martin told the New York Times that Mangione told them his spine was misaligned and “said his lower vertebrae were almost like a half-inch off, and I think it pinched a nerve.” Martin added that Mangione had confided to him about not being able to date people because of his back problem as “being physically intimate with his back condition wasn’t possible.” Martin told the Times he had texted Mangione after his surgery asking how it had gone and got the response “long story” without further details. Although the two had promised to catch up over the phone later, Mangione eventually went “radio silent.”

The Baltimore Banner reported Mangione comes “from a prominent Baltimore family.” According to the Banner, his grandfather was a self-made real estate developer who owned country clubs, nursing homes and a radio station, and that his grandmother was “a supporter of the Greater Baltimore Medical Center” and the Baltimore Opera Company. The Mangione family has owned Hayfields Country Club in Hunt Valley, Maryland—northwest of the city of Baltimore—since 1986, according to the Banner.

Luigi Mangione is related to Nino Mangione, a Republican representative in the Maryland House of Delegates, The Baltimore Sun reported Monday. The Sun reported the two are cousins who are friends on social media. Forbes has reached out to Mangione for comment. A statement issued on his social media accounts on behalf of the Mangione family said they could not comment on the news reports. “We only know what we have read in the media. Our family is shocked and devastated by Luigi’s arrest. We offer our prayers to the family of Brian Thompson and we ask people to pray for all involved.”