A new Investigation Discovery documentary takes a deep dive into Luigi Mangione, the man accused of assassinating UnitedHealthcare CEO Brian Thompson. In an In Touch exclusive sneak peek clip from Who Is Luigi Mangione?, the alleged killer’s message to federal investigators reveals his mindset ahead of the murder.

“I do apologize for any strife or traumas, but it had to be done. Frankly, these parasites had it coming,” an actor’s voice read from Mangione’s letter to federal officials at the top of the clip.

“We know when he first arrived in New York City at the end of November he visited that hotel. He was definitely casing the area,” Joseph Kenny, the New York Police Department’s Chief of Detectives explained about the Hilton Hotel in midtown Manhattan where the murder took place.

“The morning of the incident itself, we know that he was at the hotel an hour prior. As of right now we think he acted alone,” Kenny continued.

The subject matter then turned to the murder weapon.

“This was fairly trivial. Some elementary social engineering, basic CAD, a lot of patience,” the actor’s voice narrated from Mangione’s letter, referring to the computer-aided design of his gun.

“It’s a semiautomatic pistol. It had a suppressor on it that was also built on a 3D printer,” Kenny explained of the weapon. “Every time he fired, the gun would jam. So, he would have to clear the malfunction to shoot again. The recovered shell casings we had at the scene matched that gun.”

Once again, words from Mangione’s letter are read. “My tech is pretty locked down cause I work in engineering, so probably not much info there,” he wrote about how investigators likely wouldn’t find many clues about his weapon.

Kenny revealed how in Mangione’s letter, he didn’t want to use another means of assassinating Thompson, who was in Manhattan for a UnitedHealthcare shareholders meeting.

“He also discusses the contrast in whether or not using a bomb to make a statement or just killing the CEO by himself. He states that if he used a bomb, he potentially might hurt some innocent people and that would take away from his message,” the chief of detectives explained.

The clip ends with more of Mangione’s letter, where he wrote how he didn’t have time to go into greater details about the motive behind his mission. “Obviously, the problem is more complex, but I do not have space, and frankly I do not pretend to be the most qualified person to lay out the full argument,” he wrote. “But many have illuminated the corruption and greed.”

Thompson died at the age of 50 after being gunned down on December 4, 2024, while Mangione went on the run. The University of Pennsylvania graduate was later named as a person of interest in the case. Mangione, 26, was arrested on December 9, 2024, after patrons in an Altoona, Pennsylvania, McDonald’s recognized him and called authorities. The murder and the manhunt captivated the nation, as millions followed the disturbing case and all of the new developments.

Questions have lingered about why an Ivy League college graduate from a financially well-off family could turn into an alleged killer. Mangione’s mother, Kathleen Mangione, filed a missing person report with San Francisco police about her son on November 18, 2024, after months of not being able to reach him. Less than a month later, he allegedly shot Thompson

Mangione entered not guilty pleas for 11 charges, including first-degree murder, second-degree murder as a crime of terrorism and a slew of weapons charges, in Manhattan Supreme Court in New York City on December 23. If convicted of these charges, Mangione faces the possibility of life in prison without parole.

Who Is Luigi Mangione? premieres on Monday, February 17, at 8 p.m. ET/PT on Investigation Discovery.