UnitedHealthcare CEO Brian Thompson's alleged killer, Luigi Nicholas Mangione, graduated from a top Ivy League school, and now he's behind bars, charged with second-degree murder. An elite university professor explained how Ivy League campuses across the country perpetuate radicalization, painting a picture of the suspect's educational environment. 

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 national manhunt for the killer, Mangione, 26, was taken into custody on Monday at a McDonald's in Altoona, Pennsylvania.

Raised by a prominent Maryland family, the murder suspect graduated from the University of Pennsylvania with bachelor and master's degrees in computer science and was part of the Eta Kappa Nu Honor Society for Electrical and Computer Engineering.

"It is fairly uniform in the Ivy League and other so-called elite educational institutions that they skew extremely heavily to the left among the faculty," Cornell Law professor William Jacobson told Fox News Digital. "The modern Democratic Party . . . leans very heavily to the left, has a very strong anti-American, anti-capitalist wing to it . . . so it would not surprise me if somebody growing up and getting educated in that atmosphere becomes radicalized." 

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Jacobson said that there has been a shift in the attitude of educators at elite universities over the last two to three decades.

"Activism is now considered a vital part of the teaching role for many professors," he explained. "They do not distinguish between their teaching and their activism."

"That most clearly manifests itself on the anti-Israel front. But it's elsewhere, too, on the anti-capitalist front . . . if you're educating yourself in that atmosphere, I certainly could understand why someone would have hostile views towards a health insurance company."

A professor at Mangione's alma mater, the University of Pennsylvania, took to TikTok and Instagram to praise the suspect, which she has since retracted.

UPenn School of Arts and Sciences Deputy Dean Jeffrey Kallberg issued a statement to Fox News Digital on Wednesday regarding the post from UPenn Assistant English Professor Julia Alekseyeva.

"Much concern was raised by recent social media posts attributed to Assistant Professor Julia Alekseyeva," Kallberg said. "Her comments regarding the shooting of Brian Thompson in New York City were antithetical to the values of both the School of Arts and Sciences and the University of Pennsylvania, and they were not condoned by the School or the University. Upon reflection, Assistant Professor Alekseyeva has concurred that the comments were insensitive and inappropriate and has retracted them."

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Mangione subscribed to anti-capitalist and climate change causes, according to law enforcement sources, the New York Post reported. 

When the suspect 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, NYPD Chief of Detectives Joseph Kenny told Fox News. 

The Ivy League graduate had an outburst on Tuesday, as he was escorted into a Pennsylvania courthouse, revealing more of his ideology. 

"It's completely out of touch, and an insult to the intelligence of the American people and its lived experience!" Mangione shouted, as he was hurried inside. 

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A profile suspected of belonging to Mangione on the social media site Goodreads periodically posted on the platform and wrote a review for a book by the infamous Unabomber Ted Kaczynski. 

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

Writing about Kaczynski's "Industrial Society and Its Future," he quoted another online "take that [he] found interesting."

"When all other forms of communication fail, violence is necessary to survive," he wrote. "You may not like his methods, but to see things from his perspective, it's not terrorism, it's war and revolution."

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A Princeton University professor recently spoke to Fox News about an op-ed he wrote for the New York Times, in which he gave advice to college students who feel they'll be discriminated against at elite universities for being right-leaning or conservative. 

"They fear being treated unfairly by faculty members who are hostile to their beliefs," Robert George wrote. "To these students, I say, with regret: You’re right to worry. I’ve seen these things happen."

In his op-ed, he recalled a student being removed from a leadership position on a sports team because some of her more liberal teammates accused her of expressing an opinion about policing that they disagreed with.  

"That sort of atmosphere where you're surrounded by claims that the United States is not legitimate, that capitalism is a unique evil in the world, where you do not get taught the horrors of communism and socialism . . . it's not surprising that somebody would look at health care and blame an executive of a company without understanding what health care looks like in other places," Jacobson said, noting that he does not know Mangione's specific motives and cannot say definitively whether the suspect was radicalized during his studies. 

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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.

"I think people need to focus on what the evidence is, what in his background might have radicalized him . . . what in his background would have led him to engage in such an elaborate plot," Jacobson said.

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"This is not a spontaneous act of violence. This was obviously clearly planned. [The suspect] identified the person, identified the company, identified where he would be, identified when he would be vulnerable."

Fox News' Audrey Conklin and Christina Coulter contributed to this report.