Police are holding a suspect in custody in the killing of UnitedHealthcare CEO Brian Thompson, officials announced Monday.

Luigi Mangione was arrested on a gun charge after being picked up while eating at a McDonald’s in Altoona, Pennsylvania, following an employee calling the cops, the NYPD chief of detectives said. The 26-year-old had multiple fake IDs and a gun with a suppressor, according to officials.

He was also in possession of a document railing against the health care industry, a police official who has seen the document told CNN.

A backpack believed to belong to the suspect in the killing was found in Central Park on Friday, a law enforcement official said. Inside, police found Monopoly money and a jacket, according to officials briefed on the matter.

A GoodReads profile that appears to belong to Luigi Mangione shows that earlier this year, Mangione reported having read the 1995 anti-technology manifesto written by the Unabomber Ted Kaczynski, the infamous domestic terrorist and mathematician known for sending deadly bombs through the mail between 1978 and 1995.

“It’s easy to quickly and thoughtless[ly] write this off as the manifesto of a lunatic, in order to avoid facing some of the uncomfortable problems it identifies. But it’s simply impossible to ignore how prescient many of his predictions about modern society turned out,” Mangione wrote in a review of the book in January. “He was a violent individual - rightfully imprisoned - who maimed innocent people. While these actions tend to be characterized as those of a crazy luddite, however, they are more accurately seen as those of an extreme political revolutionary.”

In his review, he also wrote thoughts someone else had shared about the Unabomber in a Reddit thread online, quoting a commenter who had described Kaczynksi’s acts as “war and revolution,” saying that he “had the balls to recognize that peaceful protest has gotten us absolutely nowhere” and that “‘violence never solved anything” is a statement uttered by cowards and predators.”

Other books Mangione reported reading or wanting to read included a book about mental illness, a biography of the creator of the atomic bomb and Michael Pollan’s popular book on the science of psychedelics.

Also on GoodReads, he reported reading or wanting to read a number of books about coping with chronic back pain. An X account that appears to belong to him features a background profile photo of what looks like an X-ray image of a spine with hardware from a surgery.

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