Transcript of Suspect in CEO killing fights extradition to New York

Tonight, new details about how police say Luigi Mangione fled New York City after allegedly murdering UnitedHealthcare CEO Brian Thompson. The NYPD said they lost the shooter after he took off from the scene on an ebike into Central Park, ending up at a bus station in Uptown Manhattan. The chief of detectives now says Mangione got on the subway from there and went back downtown, revealing the details in an interview with NBC News' Jonathan Demist.

We believe he may have taken the subway back to Penn Station and then made his way to Philadelphia from there.

The chief says he then traveled west to Pittsburgh and then back east to Altoona, withdrawing money from an ATM and paying for everything with cash along the way. When Mangione was arrested 5 days after the murder, police say he had 1,000 of dollars in his bag. He also had this gun according to police. The chief laying out how the NYPD crime lab matched it to shell casings left behind at the murder scene.

That is by, an NYPD detective test firing that gun and then matching the ejection marks from the casings to the casings that we fired.

He says they still don't know where Mangione got the weapon.

The gun itself, it is a ghost gun. It is a a receiver that is comes from a gun manufacturer from parts, and then the gun was built up from a 3 d printer.

As the case takes shape against Mangione in New York, the alleged murderer remains in a Pennsylvania prison. Today, his attorney filed a petition contesting his detention, arguing Pennsylvania has not proven Mangione was in New York the day of the murder or provided probable cause that he was responsible for the crime. A hearing for extradition has been scheduled for December 30th. New York governor Kathy Hochul says she's been coordinating with Pennsylvania governor Josh Shapiro. Governor and I both want him brought back to New York as soon as possible.

And there is real concern officials say that there could be copycat violence.

This incident has created a torrent of online reactions, many of which cross over into a more uncomfortable realm of territory that we would think of as closer to threats.

The support from Mangione ranges from shared anger over the health care industry to actually being sympathetic towards the violence according to Clint Watts, an expert on cybersecurity.

What we're seeing, which is always, the most dangerous situation is people either condoning violence or maybe mobilizing to violence. That's where the concern is right now, that contagion effect that could take off.

And, Stephanie, this was a wide ranging interview with the NYPD. Did they provide any new insight into what led up to the murder?

Yeah. They did, actually, Lester. They said the family filed a missing person's report on Mangione and added that when he arrived in New York City on November 24th, that was 10 days before the murder, He knew exactly when and where that UnitedHealthcare conference was going to begin. Lester?

Alright. Stephanie Goss, thank you. Thanks for watching. Stay updated about breaking news and top stories on the NBC News app or follow us on social media.