The Manhattan District Attorney's Office in New York City confirms that Mangione has been charged with second degree murder in the death of UnitedHealthcare CEO Brian Thompson.
That's in addition to the charges he faces in Pennsylvania where he was arrested.
Legal Analyst Steven Clark says New York prosecutors will have a tactical advantage in this case.
"That extradition process to bring him back to New York can give them the time to link his DNA and fingerprints to the evidence they found at the scene in New York," says Clark.
Those who know Mangione reacted to his arrest.
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"Beyond shocked. It's unimaginable!"
R.J. Martin is a friend and former roommate of Mangione.
Martin lived with the murder suspect in a co-living space in Hawaii in recent years.
He doesn't know what may have gone wrong, but is well aware of Mangione's back problems, and a recent surgery that Mangione had.
"I knew he was going to have a surgery so earlier this year I checked in with him. 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," said Martin.
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A high school acquaintance of Mangione, who didn't want to be identified, said he knew something wasn't right with the Ivy League scholar several months ago saying quote, "The only time he really came back up into my life was around 6 months ago. I had heard that his family members were reaching out to different classmates of mine and they were inquiring about his whereabouts."
Online there are actually thousands of comments in support of Mangione, who worked at Stanford as a head program counselor back in 2019. Some online saying he didn't do it, others talking negatively about corporate America.
"In a very disturbing way this young man has become almost a folk hero online for the way he conducted this homicide and I think prosecutors want to send the message that you may have a grievance with the health care industry or corporate America but you cannot do this type of act," said Clark.
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Mangione's family issued a statement Monday saying they are quote "shocked and devastated by Luigi's arrest."
Law enforcement sources tell ABC News they found Mangione with writings saying quote "These parasites had it coming" and "I do apologize for any strife and trauma, but it had to be done."
That said, Clark tells us the defense will likely take a long look at Mangione's mental state.