CEO killing latest: Writings show Mangione fixated on company for months, sources say

Writings seized from Luigi Mangione, the suspect accused of gunning down UnitedHealthcare CEO Brian Thompson, indicate he had been developing a fixation and increasing malice toward the company and allegedly talking about harming its leader for months, according to law enforcement sources.

That fixation would eventually evolve into an alleged plan to shoot that CEO, the sources said.

Some of the entries in the notebook seized from Mangione upon his arrest in Pennsylvania earlier this week had dates on them going back to mid-2024, the sources said.

Some of the writings were diary-style, documenting how he felt, what he did that day, and also documented a desire to focus on his health and himself, and find his purpose, the sources said.

Then, as time went on -- as Mangione allegedly fell out of contact with friends and family and grew increasingly isolated -- some of his writings indicated a deterioration in his thinking and state of mind, illustrating a gradual build towards the alleged plan to kill UnitedHealthCare's CEO at their "annual parasitic bean-counter convention," sources said.

Mangione, 26, was apprehended in Altoona, Pennsylvania, on Monday, nearly one week following the Dec. 4 slaying in New York City.

The suspect left New York City following the shooting by train, and not by bus as first thought, police sources told ABC News.

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 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," he said. "We will be ready, whether he is going to waive extradition or whether he is going to contest extradition."

The FBI's New York Field Office said Friday that among the multiple tips the agency received was a tip from police in San Francisco "regarding the possible identity of the suspect." The FBI said it "conducted routine investigative activity and referred this and other leads to the New York City Police Department."

The NYPD previously said none of the hundreds of tips it received included Mangione's identity.

The NYPD confirmed Friday it received the FBI tip but that it was not passed along by the agency in a manner that distinguished it as being from another law enforcement agency.

The tip was subsequently not prioritized the way it might have been had NYPD detectives known it was coming from another police department, the NYPD said.

The NYPD had dispatched detectives to Georgia to follow leads that came in from Atlanta police. The NYPD did not do that kind of follow-up with the San Francisco tip because, an NYPD source said, of the way it was passed along by the FBI.

New York City Mayor Eric Adams said Friday he believes Mangione was radicalized while he attended the University of Pennsylvania.

"Here you have a young man who went to an 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."

Mangione's writings, obtained by ABC News, claimed that the U.S. has the most expensive health care system in the world, but ranks about No. 42 in life expectancy. He said UnitedHealthcare "has grown and grown, but as our life expectancy? No the reality is, these [indecipherable] have simply gotten too powerful, and they continue to abuse our country for immense profit."

"I do apologize for any strife of traumas but it had to be done," he allegedly wrote. "Frankly, these parasites simply had it coming."

Neither Mangione nor his parents received insurance through UnitedHealthcare, according to UnitedHealth Group.

Thompson's murder ignited online anger at the health insurance industry and some people online have celebrated Mangione. Supporters of Mangione have donated money to a defense fund established for him, leaving law enforcement officials worried Mangione is being turned into a martyr.

Adams attributed the support Mangione is receiving to "anger and pain."

"People know how challenging it is navigating our health care system on many levels, the cost of health care 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."

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.

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.