At first, investigators believed Mangione had boarded a bus at the Port Authority terminal by the George Washington Bridge, where investigators said he was spotted on security cameras being dropped off by a taxi. There was no imagery of Mangione actually getting onto a bus.
Now, police sources say there's video evidence that shows Mangione left the George Washington Bridge bus station, went south to Penn Station and left New York City by train to Philadelphia.
Pennsylvania authorities have said Mangione then spent several days traversing the state from Philadelphia to Pittsburgh.
Mangione was apprehended in Altoona, Pennsylvania, on Monday after nearly one week on the run following the Dec. 4 slaying.
Mangione, 26, is in custody at a Pennsylvania state prison after a judge denied bail on Tuesday.
In Pennsylvania, Mangione faces charges including allegedly possessing an untraceable ghost gun. In New York, he faces charges including second-degree murder.
Mangione may waive extradition to New York City as early as Tuesday, Manhattan District Attorney Alvin Bragg said on Friday.
"Indications are that the defendant may waive but that waiver is not complete until a court proceeding," Bragg said.
The earliest a court proceeding could be scheduled in Pennsylvania is Tuesday, Bragg said.
"So until that time, we are going to continue to press forward on parallel paths. We will be ready, whether he is going to waive extradition or whether he is going to contest extradition," the district attorney said.
Mayor Eric Adams said Friday that Mangione was radicalized at the University of Pennsylvania.
"Here you have a young man who went to Ivy League school, came from an affluent background and family, had all the things that many Americans would like to have. But he found himself hating corporations and hating other things," Adams said on GMGT Live's "The Reset Talk Show." "We're radicalizing our children in general, but specifically on these Ivy League campuses."
Adams attributed the support Mangione is receiving to "anger and pain."
"People know how challenging it is navigating our healthcare system on many levels, the cost of healthcare system. Some of the denials, some of the of illnesses that are not covered. And all across America, people have experienced that disappointment. And so you're seeing a response to that," Adams said. "And we can't send a signal that if you're angry over something, if you're angry because you got a parking ticket, you respond with violence."
RELATED | Supporters of suspected CEO killer Luigi Mangione establish defense fund
It comes as it was revealed that Mangione wasn't a member of the insurer, a company spokesperson said.
"Brian Thompson's killer was not a member of UnitedHealthcare," the company told ABC News.
Prosecutors at the Manhattan District Attorney's Office have begun presenting evidence to a grand jury as they work to secure an indictment against Mangione for the killing of Thompson, sources told ABC News.
The 26-year-old Ivy League graduate remains in custody at a Pennsylvania state prison after a judge denied bail on Tuesday. His next court date in Pennsylvania is Dec. 30.
"He has constitutional rights and that's what he's doing" in challenging the interstate transfer, defense attorney Thomas Dickey told reporters on Tuesday.
Authorities are still looking to access a phone recovered by police in an alley following the shooting that is believed to be linked to the suspect, sources said Thursday. Police have obtained a search warrant for the phone, sources said.
RELATED | UnitedHealthcare CEO killing: NY prosecutors presenting evidence to grand jury, sources say
At least two other search warrants have been issued so far in the New York case. They include to search the hostel where the suspect stayed in New York City, as well as the backpack containing Monopoly money and a jacket that was found in Central Park and is believed to belong to him, sources said.
On Friday, the FBI's New York Field Office said it passed along a tip from San Francisco police, who said they recognized the suspected Midtown shooter from a prior missing persons report filed by his mother.
"FBI New York conducted routine investigative activity and referred this and other leads to the New York City Police Department as part of our assistance to them in their investigation," FBI New York said in a statement. "Extensive sharing of the photos by law enforcement led to the identification by a citizen and subsequent arrest by the Altoona Police Department."
An NYPD official says general Information about Mangione's possible identity was passed along by FBI, but not in an urgent manner or in a way that distinguished it as a credible tip from San Francisco police.
The NYPD had previously said it had not received any about Mangione's identity before he was captured in Altoona, Pennsylvania.
Three shell casings recovered outside the Midtown Manhattan hotel where Thompson was fatally shot match the gun allegedly found on Mangione when he was arrested, police announced Wednesday.
Fingerprints recovered from a water bottle and a Kind bar near the crime scene have also been matched to Mangione, police said.
Meanwhile, the search for the e-bike Mangione abandoned as he fled last week's shooting has never been found.
Mangione ditched the bike on the Upper West Side following the murder, hailing a taxi at 86th Street and Amsterdam Avenue to the George Washington Bridge Bus Station.
A working theory is someone spotted it abandoned and swiped it.
RELATED | Timeline of UnitedHealthcare CEO shooting
How police tracked down CEO murder suspect Luigi Mangione
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