Luigi Mangione, the 26-year-old former Ivy Leaguer who allegedly abandoned a career in computer science to assassinate UnitedHealthcare CEO Brian Thompson, is facing increasing legal troubles as state and federal prosecutors continue to up the charges against him and reveal new evidence.

A new federal criminal complaint alleging charges of stalking, murder through use of a firearm and federal firearms offenses accuses Mangione of keeping a journal in which he outlined the deadly plot, mused about choosing a victim and patted himself on the back for continuing to research the target.

The new federal case brings the potential for the death penalty back into the equation, should Mangione be convicted.

“This investor conference is a true windfall,” one of the entries reads, according to the affidavit. “And – most importantly – the message becomes self-evident.”

UNITEDHEALTHCARE CEO MURDER SUSPECT LUIGI MANGIONE FACING NEW CHARGES IN NEW YORK

Mangione allegedly wrote about wanting to “wack” an insurance CEO and that he was “glad – in a way – that I’ve procrastinated, [because] it allowed me to learn more about UHC.”

He allegedly wrote that he chose to target the insurance industry because “it checks every box.”

Then he allegedly shot Thompson in the back outside a Hilton hotel in Manhattan, where UnitedHealthcare was slated to host its annual shareholder conference later that morning on Dec. 4.

“The radicalization that is taking place across our country, we cannot ignore,” NYC Mayor Eric Adams said Thursday after Mangione landed in Manhattan after being flown in from Pennsylvania. “When you see an incident that took place on our streets, when you witnessed the shooting that took place on a school campus, by now, a young girl that is the continuation of our young people are crying out for help. We have an obligation not only to make apprehensions after an incident of this magnitude, but to do far more to prevent.”

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Assistant FBI Director James Dennehy also slammed Mangione’s allegedly twisted morality.

“Luigi Mangione allegedly conducted the carefully premeditated and targeted execution of Brian Thompson to incite national debates,” he said in a statement. “This alleged plot demonstrates a cavalier attitude towards humanity – deeming murder an appropriate recourse to satiate personal grievances

The document includes surveillance images that purport to show the suspect approaching and fleeing the scene, the moment of the murder, and the suspected murder weapon and 3D-printed suppressor.

Read the federal criminal complaint

UNITEDHEALTHCARE CEO MURDER SUSPECT LUIGI MANGIONE INDICTED IN NEW YORK

The affidavit also alleges that Mangione wrote a letter addressed “to the Feds.”

“I wasn’t working with anyone,” the journal reads. “This was fairly trivial: Some elementary social engineering, basic CAD, a lot of patience.”

CAD is an acronym for computer-aided design. Social engineering is a technique that hackers use to trick people into divulging information to someone who isn’t authorized to receive it.

Mangione obtained both a bachelor’s and master’s degree in computer science from the University of Pennsylvania at the same time, then went on to work as a computer programmer before sources say he fell out of touch with his parents over the summer and resurfaced in New York City earlier this month in connection with the Thompson slaying.

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“P.S. you can check serial numbers to verify this is all self-funded,” the Feds letter continued. “My own ATM withdrawals.”

Investigators allegedly recovered about $10,000 in cash during Mangione’s arrest by police in Altoona, Pennsylvania. He denied it was his in court.

His defense team, however, argued that New York’s first-degree murder charge, which includes an allegation of terrorism, is an overreach. The federal charges go even further.

“The federal government’s reported decision to pile on top of an already overcharged first-degree murder and state terror case is highly unusual and raises serious constitutional and statutory double jeopardy concerns,” his New York defense attorney, Karen Friedman Agnifilo, told Fox News. “We are ready to fight these charges in whatever court they are brought.”

The federal complaint repeats some details stated by Manhattan prosecutors and the NYPD and lays out a clear timeline.

Mangione allegedly came to New York from Atlanta, Georgia, arriving at the Port Authority Bus Terminal in Manhattan around 10 p.m. on Nov. 24. The first place he went from there was to the Midtown Hilton hotel where the murder would take place, according to authorities. Then he took a cab to a hostel on the Upper West Side.

He checked in under the fake name “Mark Rosario,” according to court documents, showed a fake ID and paid cash. However, when a clerk at the hostel asked him to take off his mask so she could see his face, he did – in front of a surveillance camera. That image circulated widely after the NYPD asked for the public’s help identifying a suspect and ultimately led to Mangione’s arrest.

The entire rest of the time he spent in New York, the suspect “consistently kept his mask on…including while inside the hostel.”

On the day of the murder, Dec. 4, Mangione allegedly left the hostel carrying a gray backpack and riding an electric bike around 5:35 a.m. Police used multiple surveillance cameras to track his route from the Upper West Side to the Midtown Hilton.

Around 5:41 a.m., Mangione was allegedly seen walking near the crime scene and making a purchase at a nearby coffee shop. 

“On at least one occasion, prior to the murder, the Shooter was depicted using a cellphone,” according to the affidavit. 

At around 6:45 a.m., Thompson arrived outside the hotel. Mangione had allegedly been waiting for nearly an hour. He allegedly gunned down the victim, fled on foot to West 55th Street, got on the electric bike and rode north. He disappeared into Central Park for an unspecified time period and emerged near West 77th Street and Central Park West, riding the bike but without the gray backpack.

Just before 7 a.m., he ditched the bike, and within minutes hailed a taxi that drove him to the George Washington Bridge Bus Terminal in Upper Manhattan. A surveillance camera in the taxi took a picture of his masked face.

Surveillance video shows a gunman step out from between two parked cars, walk up behind Thompson and shoot him from behind, striking him in the back and the leg. Thompson’s expected presence at an investor conference scheduled for 8 a.m. that morning had been public information. 

Police recovered spent shell casings and at least one live round with the words “deny,” “delay” and “depose” written on them – a possible reference to a book that was critical of the insurance industry.

“I respectfully submit that MANGIONE is the Shooter who shot and killed the Victim on December 4, 2024,” an FBI agent wrote in the affidavit. “Additionally, the Notebook entries, the Feds Letter, the Shooter’s apparent surveillance of the Midtown Hotel on November 24, 2024 and December 4, 2024, and the Shooter’s use of countersurveillance techniques and escape from New York City all suggest that the Shooter undertook extensive efforts to identify the Victim, place the Victim under surveillance, and track the Victim’s whereabouts in the time period leading up to the murder.”

The federal charges include two counts of stalking, travel in interstate commerce and use of interstate facilities, murder through use of a firearm and a federal firearms offense. They come shortly after Mangione was indicted on first- and second-degree murder and domestic terror charges in New York.

“Manhattan DA Alvin Bragg was handling three of the biggest trials in the country: the Trump hush money case, Daniel Penny, and Mangione, but Trump’s newly appointed Attorney General and Manhattan U.S. Attorney will be swooping in shortly,” said Neama Rahmani, a former federal prosecutor who now runs a private practice that frequently places him on the opposite side of insurance companies like UnitedHealthcare in court.

“Federal charges change the game. New York doesn’t have the death penalty, but the federal government does. The feds may be trying to send a message to Mangione to take a plea to take the death penalty off the table.”

Speaking after Mangione’s first appearance in federal court, acting U.S. Attorney for the Southern District of New York Edward Kim said that, at least for now, he expects the state case to proceed before the federal one.

Authorities in New York and Pennsylvania have both condemned widespread online support for Mangione, who is accused of sneaking up on a father of two and shooting him from behind with a handgun and homemade silencer. 

“Luigi Mangione is now formally charged and indicted for murder, and let me be perfectly clear, in the nearly two weeks since Mr. Thompson’s killing, we have seen a shocking and appalling celebration of cold-blooded murder,” NYPD Commissioner Jessica Tisch told reporters Wednesday. “Social media has erupted with praise for this cowardly attack.”

Mangione was taken to a Manhattan federal court after arriving in New York. His lawyers declined to comment after the hearing.

“Respectfully decline to make any comment at this point,” Friedman Agnifilo told reporters. “Mangione appreciates support.”

Fox News’ Maria Paronich contributed to this report.