(NEW YORK) -- He was an Ivy League graduate and the valedictorian of his class at a private all-boys high school in Baltimore, where his wealthy family is prominent in the real estate business and owns country clubs and golf courses. Despite having a privileged background, Luigi Mangione was described by friends as "humble" and believed to be destined for a "bright future."
But all that changed on Monday when the 26-year-old Mangione was named by police as the prime suspect in the brazen targeted shooting of UnitedHealthcare CEO Brian Thompson that unfolded in the middle of New York City and captured the nation's attention.
"He was absolutely not a violent person as far as I could tell," R.J. Martin, Mangione's former roommate, told ABC News.
Martin said Mangione's arrest in the murder case was "beyond shock."
"It's unimaginable," Martin said.
Mangione was charged Monday night with second-degree murder in the killing of 50-year-old Thompson.
Investigators suspect that Mangione held a grudge against the medical insurance agency and may have been inspired by Ted Kaczynski, the mathematician-turn-domestic terrorist known as the "Unabomber" who blamed technology for a decline of individual freedom and mailed handcrafted explosives to targeted individuals between 1978 and 1995.
As police were escorting Mangione into a court hearing Tuesday in Hollidaysburg, Pennsylvania, he yelled to reporters gathered at the scene, "It is completely out of touch and an insult to the intelligence of the American people" before officers wrestled with him and hustled him into the courthouse.
Thompson, who lived in Minnesota, was walking alone on a Midtown Manhattan sidewalk around 6:40 a.m. last Wednesday, heading to his company's shareholders conference at the New York Hilton, when a mask and hooded gunman was captured on surveillance cameras lying in wait. The shooter calmly pulled out a 3D-printed ghost gun equipped with a silencer and opened fire from behind, police said.
After an intense five-day manhunt that took police to multiple states, Mangione was arrested at a McDonald's in Altoona, Pennsylvania, when a customer recognized him from surveillance photos and alerted an employee of the fast-food chain who called 911.
Altoona police officers confronted Mangione, who was wearing a medical mask and sitting alone at the rear of the McDonald's looking at a laptop. They wrote in a criminal complaint that when they asked Mangione whether he had recently been in New York City, the suspect "became quiet and started to shake."
During a news conference following the arrest, Altoona police officer Tyler Frye said he and his partner asked the man to pull down his mask.
"As soon as we pulled that down, or we asked him to pull it down, me and my partner recognized him immediately, just from what we saw in the media with photos, videos, we just didn’t even think twice about it. We knew that was our guy," Frye said.
Document found on suspect 'speaks to both motive and mindset'
Mangione appeared in court Monday night in Pennsylvania, where he was charged with illegal possession of a firearm and fraudulent pieces of identification. During his arrangement, the defendant, who appeared in court without an attorney, offered insight into his family history, suggesting he has been estranged from his relatives in recent months.
Despite his family's wealth and prestige in the Baltimore area, Mangione requested on a court form that a public defender represent him. Though he has since retained a defense attorney, Thomas Dickey.
When a judge asked if he had been in touch with his family, Mangione said he was in touch "until recently."
A Pennsylvania prosecutor asked the judge to hold Mangione without bail, saying the defendant had several thousand dollars in cash on him at the time of his arrest.
Mangione asked the judge to "correct" details the district attorney shared in court, specifically about how much money he had on him.
"I don't have that much money," he said, suggesting the cash was "a plant or something."
Document speaks to 'motivation': Police
In a backpack Mangione had with him, police allegedly found a black 3D printed pistol and a black silencer, which was also 3D printed, that appears to match the weapon used to kill Thompson, according to the criminal complaint. They also discovered a three-page document on Mangione that NYPD Commissioner Jessica Tisch said "speaks to both his motivation and mindset."
In an interview Tuesday on ABC's "Good Morning America," NYPD Chief of Detectives Joe Kenny said the handwritten document from Mangione may shed light on why the executive of the country's biggest insurance company was targeted.
"He does make some indication that he's frustrated with the healthcare system in the United States, specifically he states how we are No. 1 most expensive healthcare system in the world ... he was writing a lot about his disdain for corporate America," Kenny said.
Sources with knowledge of the document told ABC News that UnitedHealthcare was mentioned in the document, but Tisch said it remains under investigation if Mangione has a personal connection to the healthcare giant.
Law enforcement sources also told ABC News that the document says "These parasites had it coming" and "I do apologize for any strife and trauma, but it had to be done."
Mangione "appeared to view the targeted killing ... as a symbolic takedown and a direct challenge to its alleged corruption and 'power games,'" according to a confidential assessment by the NYPD intelligence bureau and described to ABC News by a source. Mangione allegedly described himself as the "first to face" UnitedHealthcare "with such brutal honesty," according to the assessment.
Among the writings recovered in a spiral notebook were alleged plans concocting how to eventually kill the UnitedHealthcare CEO, according to law enforcement officials.
"What do you do? You whack the CEO at the annual parasitic bean-counter convention," one passage allegedly said, according to the officials.
The notebook also allegedly makes reference to the Unabomber, but the writings said that using explosives could "risk innocents," according to the officials.
Detectives are still examining Mangione's writings but are considering the contents of the notebook to represent a confession, sources said.
To plead not guilty
Dickey told reporters on Tuesday that Mangione will plead not guilty to the Pennsylvania charges. He said he anticipates that Mangione will also plead not guilty to the second-degree murder charge in New York.
The attorney said he has limited information about the facts of the New York murder case but he conceded Mangione is "accused of some serious matters." He added that Mangione is "taking it as well as he can."
Dickey told ABC News' "Good Morning America" on Wednesday that he had "not been made aware of any evidence that links the gun that was found on his person to the crime."
"A lot of guns look the same," Dickey said. "If you brought a gun in and said, 'Well, it looks like that,' I don't even know if that evidence would be admissible. And if so, I would argue that it wouldn't be given much weight."
Dickey also cautioned that anyone speculating on the case should take the potential evidence "in its entirety," not taking pieces of writing or other evidence "out of context."
Family 'shocked and devastated'
As investigators sift through Mangione’s online activity, they are examining multiple social media posts that suggest he may have suffered a major back injury including a photo of an X-ray of a spine posted on X and at least two books about back injuries on his Goodreads profile.
Martin told ABC News that he was aware of Mangione's back surgery.
"I knew he was going to have a surgery so earlier this year I checked in with him," Martin said. "He confirmed to me that he had had the surgery and he sent me X-rays. It looked heinous with giant screws going into his spine."
Another high school classmate of Mangione, who asked not to be identified, told ABC News that the suspect had undergone back surgery in recent months.
"Whether it was complications from his back surgery or personal issues with his family and the healthcare system, it definitely came as a huge huge surprise just because he's not the type of person to do this without reason," the classmate said.
Mangione's family released a statement Monday saying they are "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," Mangione's cousin, Maryland Republican Delegate Nino Mangione, who represents parts of Baltimore County, wrote on X on behalf of the family.
Mangione's extended family owns Hayfields Country Club in Hunt Valley, Maryland, Turf Valley Resort in Ellicott City, Maryland and WCBM, an AM talk radio station based out of Owings Mills, according to ABC affiliate station WMAR.
High school valedictorian
In Baltimore, Mangione attended Gilman School, an all-boys private school with an annual tuition of nearly $40,000. He was the valedictorian of his 2016 graduating class.
"The class of 2016's inventiveness also stems from its incredible courage to explore the unknown and try new things," Mangione said in his valedictorian speech.
The school said in a statement that Mangione's "suspected involvement in this case is deeply distressing news on top of an already awful situation."
The friend who asked not to be identified said Mangione "was not a problematic kid" in high school.
"In high school, he'd never really got into trouble, was not attention seeking or anything like that. Just a bright kid with a bright future," the friend said.
Mangione is a May 2020 graduate of the University of Pennsylvania, according to a school spokesperson. He studied computer science and earned bachelor's and master's degrees in engineering from the Ivy League institution.
Following his graduation, Mangione worked as a data engineer at online car marketplace TrueCar, Inc. beginning in November 2020, according to a LinkedIn account that appears to belong to Mangione.
A representative for TrueCar said that Mangione stopped working for the company in 2023.
Mangione's last known address was in Honolulu, Hawaii, where he was arrested in November 2023 for trespassing in a Hawaii state park, court records show. He pleaded no contest and was ordered to pay a $100 fine.
NYPD officials said a background check of Mangione has, so far, uncovered no other criminal in New York and throughout the rest of the country.
Mangione also has ties to San Francisco, where in 2019 he worked as a head program counselor at Stanford University, according to a school representative.
His family was searching for him
The friend who asked not to be identified said Mangione fell off the radar of his family and friends about six months ago.
The classmate said he was notified by other classmates that Mangione's family was "inquiring about his whereabouts."
Mangione's mother filed a missing person report in November with the San Francisco Police Department, seeking information on her son's whereabouts, two law enforcement sources told ABC News. Both the San Francisco police chief and a spokesperson for the department referred further questions about that inquiry to the NYPD.
"I didn't hear anything about him until today when all the news dropped," the friend said on Monday. "It really sucks for his family, who must be going through it right now."
Unabomber manifesto review
A Goodreads account that appears to belong to Mangione left a four-star review on Ted Kaczynski's "Industrial Society and Its Future" -- more commonly known as the "Unabomber manifesto."
In the review, Mangione described Kaczynski as "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," Mangione wrote.
A source confirmed to ABC News that the Goodreads account is part of the law enforcement investigation.
According to the NYPD intelligence analysis conducted in the case, "Mangione may have found inspiration in Ted Kaczynski -- the violent, anti-technology extremist known as the Unabomber -- echoing in his note and reflecting in his targeting a similar mindset of the need for unilateral action to bring attention to abusive corporate actions."
This story has been updated.
ABC News' Peter Charalambous, Madison Burinsky, Kate Holland, Chris Looft, Sabina Ghebremedhin, Kaitlyn Morris, Hannah Prince and Alexandra Myers contributed to this report.
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