Family and friends reacted with shock and disbelief after Luigi Mangione, a 26-year-old Ivy League graduate, was identified as the suspect in the murder of UnitedHealthcare CEO Brian Thompson.

Mangione was taken into custody at a McDonald's in Pennsylvania on Monday following a dayslong manhunt after an individual at the establishment thought he bore a resemblance to the suspect being sought in the fatal shooting of Thompson last week outside a hotel in Midtown Manhattan. He has since been charged in New York with second-degree murder in what police have said is a targeted, premeditated attack.

"Our family is shocked and devastated by Luigi's arrest," Mangione's family said in a statement. "We offer our prayers to the family of Brian Thompson and we ask people to pray for all involved."

"We are devastated by this news," the statement added.

The Gilman School, a private school in Baltimore from which Mangione graduated as valedictorian in 2016, said his "suspected involvement in this case is deeply distressing news on top of an already awful situation."

"Our hearts go out to everyone affected. Here on campus, our focus will remain on caring for and educating our students," the statement continued.

A classmate who graduated from Gilman with Mangione told ABC News that Mangione "is the last person I expected to be involved in something like this."

"He always came off as a really good kid, very nice, very humble, open to talk to anyone," the classmate said. "Really not a problematic kid in high school. He never really got in trouble, wasn't attention-seeking or anything like that. Just a bright kid with a bright future, is kind of what I thought."

Mangione went on to study computer science at the University of Pennsylvania and graduated with bachelor's and master's degrees in engineering. It was "expected that he would go down like a typical path," the classmate said.

"So when we heard about all of this, it came as a huge shock to us, and honestly, like our whole community," the classmate said.

About six months ago, the classmate said he heard from other classmates that Mangione's family was "inquiring about his whereabouts."

"I heard that he got back surgery so we were all a little worried and many people reached out to him. No response," the classmate said. "I didn't hear anything about him until today when all the news dropped."

"Huge shock, definitely," they added.

Mangione's last known address was in Honolulu, police said. R.J. Martin, the founder of a co-living space for remote workers in Honolulu who said he was Mangione's roommate there, said he was "beyond shocked" by the news.

"It's unimaginable," Martin told Honolulu ABC affiliate KITV.

"Never once talked about guns, never once talked about violence," Martin told the station. "He was absolutely a not violent person, as far as I could tell."

Martin also recalled that Mangione had a back injury after a surf lesson and needed surgery.

He said they would talk about issues like health care, housing and food systems but "it wasn't anything specific."

"It wasn't like he had an ax to grind," he said.

When Mangione was arrested on Monday he had "written admissions about the crime" with him, according to the New York arrest warrant.

The suspect had several handwritten pages on him that appeared to express a "disdain for corporate America" and to indicate "he's frustrated with the health care system in the United States," NYPD Chief of Detective Joe Kenny told ABC News' "Good Morning America" on Tuesday.

Mangione considered the killing of Thompson to be a "symbolic takedown" of UnitedHealthcare over perceived corruption, according to a confidential assessment of the crime by the NYPD intelligence bureau described to ABC News. The assessment is based in part on the suspect's writings.

It is unknown if Mangione has a personal connection to UnitedHealthcare, NYPD Commissioner Jessica Tisch said.

In addition to murder, Mangione was charged in New York with possession of a loaded firearm, possession of a forged instrument and criminal possession of a weapon.

He was also charged with carrying a gun without a license, forgery, falsely identifying himself to authorities and possessing "instruments of crime" in Pennsylvania, where he remains in custody and is challenging extradition to New York.

Defense attorney Thomas Dickey, who was retained by Mangione in the Pennsylvania case, said his client is refusing to waive extradition because it is his constitutional right to do so.

"He has constitutional rights and that's what he's doing," Dickey said. "If you believe in America and that presumption of innocence, you can't rush to judgment."

Dickey 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."

ABC News' Aaron Katersky, Peter Charalambous and Sabina Ghebremedhin contributed to this report.