UnitedHealthcare CEO Brian Thompson's alleged killer, once a private school valedictorian and an Ivy League graduate, may have been triggered by his age and an Obamacare provision, according to a former investigator.

Thompson, 50, was shot from behind on the sidewalk outside a New York City Hilton hotel on Dec. 4 before a shareholder conference. After a five-day manhunt for Thompson's killer, Luigi Nicholas Mangione, 26, was taken into custody on Monday at a McDonald's in Altoona, Pennsylvania.

"He's 26 years old, which is the year you get kicked off your family's insurance claim," retired FBI agent Scott Duffey told Fox News Digital. "Was he well insured or was he not? Those are the things that I would be asking as an investigator."

Obamacare, also known as the Affordable Care Act, requires health plans that offer dependent child coverage to make the coverage available until the adult child reaches the age of 26, according to the U.S. Department of Labor. 

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"I'm not so sure he has remorse," Duffey added. "I feel like whatever took place in his life relatively soon… he made a conscious decision to go down this road."

NYPD Chief of Detectives Joseph Kenny said Mangione may have sustained a back injury on July 4, 2023.

"He was posting an X-ray on his social media. Some of the writings that he had, he was discussing the difficulty of sustaining that injury," Kenny told Fox News on Tuesday. "So we're looking into whether or not the insurance industry either denied a claim from him or didn't help him out to the fullest extent."

Duffey said he wonders when Mangione made the "turn" that led to his downfall, adding, "was it when he got into some sort of physical ailment and then perhaps medication…realized just how people are suffering and then got this guilt trip that… 'I've got to change the world?' Or did he suffer some sort of mental break?" 

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Mangione was arrested after a McDonald's customer and employee spotted him and thought he matched the suspect on a wanted poster. 

"I'm struck with…how does somebody who seems to be so intelligent make such stupid mistakes? He's caught because of a great caller…and that's all it took…that blows my mind," Duffey said. "So is it such arrogance that he couldn't see right before him? ‘How am I going to get out of this? Let me use some of my ingenuity.’" 

"If he was in New York City or Philadelphia or another major city, I think he would've remained obscure. But he went to Altoona…it is, from what I've gathered… a hometown feel. He obviously didn't fit in," the retired agent added. "And you've got people saying 'you're not from around here.'" 

Prosecutors said the 26-year-old was found with $8,000 in U.S. cash, $2,000 in foreign currency, masks and a passport.

"I just don't feel like he was done yet with whatever he was seeking out to do," Duffey added. "Definitely making a name for himself… just retribution or whatever it is that he felt like he owed society."

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Mangione has been charged with second-degree murder, second- and third-degree criminal possession of a weapon, and second-degree criminal possession of a forged instrument in the killing of Thompson, according to a felony arrest warrant in New York.

Details have surfaced about the murder suspect's history, showing he had a seemingly model education. 

Mangione graduated from the elite Gilman School, a private high school in Baltimore, at the top of his class, and he delivered the commencement speech at his graduation ceremony. 

Classmates at the private high school once described him as being the "best at pick-up lines," his yearbook, obtained by SNWS, shows. 

He went on to graduate from the University of Pennsylvania with bachelor and master's degrees in engineering and was part of the Eta Kappa Nu Honor Society for Electrical and Computer Engineering.

"He seemed to have a fantastic social quality…those that were close to him are saying that this was your all around guy,"  Duffey said. "I did watch his valedictorian speech… well spoken, well thought out…a senior in high school, who seemed to have high ambitions, a great sense of humor… it just seemed like he was everything."

"Then I look at the moment that he's approached by law enforcement, and there are so many missteps."

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When officers approached Mangione before his arrest, he was wearing a medical mask, and he allegedly handed over a fake ID and gave a phony name, according to court documents. When police asked if he'd recently been to New York, Mangione allegedly "became quiet and started to shake." 

When he was taken into custody, four fake IDs, a gun and silencer resembling those used in the shooting, and a handwritten manifesto denouncing the health insurance industry were found on him. 

In his manifesto, Mangione mentioned UnitedHealthcare specifically, Kenny said.

Duffey explained how the alleged killer's engineering studies may have played a part in his planning of the attack and ultimate capture. 

"Regardless of what type of engineering you're in, the mind is able to piece together, and you're able to see the big picture. You've got to figure out both on paper, and then of course, executing a plan," he said. 

"The engineering mind…is fantastic at putting together puzzles," Duffey added. "But I've always said, any time I talk about a criminal, they're so good at putting in the pre-planning and not the exit strategy. And ultimately, that is their demise."

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Mangione was a periodic poster on the social media site Goodreads, and he wrote a review for a book by the infamous Unabomber Ted Kaczynski. 

"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," Mangione wrote in his review. "But it's simply impossible to ignore how prescient many of his predictions about modern society turned out."

Duffey said he believes Mangione "did his homework" in choosing the Unabomber, specifically. 

"I don't think it's an accident of all the serial killers out there, of all the individuals who have a manifesto…he aligns with Ted Kaczynski," Duffey said. "Kaczynski was arrogant in the sense that …can everybody else not see what I'm seeing with regards to society."

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Mangione will fight extradition to New York, but Manhattan District Attorney Alvin Bragg's office has vowed to get the murder suspect to New York City to face justice as fast as possible. 

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"Profilers talk about …what makes people tick and do the things they do," Duffey said. 

"It ultimately comes down to idealizing, turning it into a fantasy. And that fantasy just controls your everyday thoughts, and then ultimately … you commit the act that you fantasized about."

Fox News' Michael Ruiz contributed to this report.