Lead Mangione detective says silencer found in case was unlike anything he'd seen in 25 years

In a recent interview, a retired NYPD detective who was involved in the investigation of UnitedHealthcare CEO Brian Thompson’s assassination described the silencer used in the crime as uniquely sophisticated, highlighting the calculated nature of the murder. This aligns with investigators’ assessment of the methodical planning involved in Thompson’s killing.

Retired NYPD Detective Sergeant John Griffin shared with “Dateline” that, throughout his 25-year career, he had never encountered a silencer like the one used in this case.

“It had an unusual front attachment, resembling a makeshift suppressor or silencer,” explained Griffin, who served in the NYPD’s major crimes unit.

Luigi Mangione, aged 28, faces allegations of murdering Thompson, a 50-year-old father from Minnesota. The incident occurred as Thompson was shot outside a Manhattan Hilton hotel, captured on video, just before an investor conference on December 4, 2024.

Luigi Mangione was seen attending an evidence suppression hearing at the Manhattan Supreme Court in New York City on May 18, 2026. (Photo by Jeenah Moon/Reuters)

Pat Diaz, a private investigator who spent 30 years as a homicide detective in the Miami area, told News Agency Monday that silencers were a big part of the violent “Cocaine Cowboys” and mafia era of the 1980s and 1990s.

“Usually on major drug killings, they’d just drop the weapon there, because most of the time they were untraceable,” he said. “It wasn’t unusual in the ’80s, ’90s, to come up with a firearm with a silencer on it — especially in Miami.”

Stricter laws diminished their use in more recent decades, but they are making a resurgence, he said.

Brian Thompson, CEO of UnitedHealthcare, is shown in an undated portrait provided by UnitedHealth. He was shot and killed on his way to an investor conference in New York City in what prosecutors described as a politically motivated assassination. (AP Photo/UnitedHealth Group via AP)

The 3D-printed version shows some capability with mechanical engineering as well as intent, he added.

“It shows his frame of mind,” Diaz said. “Insanity is out the door, because he was of sound mind to be able to engineer and design a silencer.”

Typically, a printed device requires multiple components to be created and then assembled — then fitted to the weapon safely.

A split image showing Luigi Mangione in court and his alleged handgun and 3D-printed silencer. Mangione is accused of assassinating UnitedHealthcare CEO Brian Thompson. (Curtis Means/Pool via Reuters)

The former Ivy Leaguer has pleaded not guilty to state and federal charges in connection with the case and could face life in prison without parole if convicted on the most serious federal charges.

In New York, he faces a maximum penalty of life imprisonment if convicted, which would include a chance of parole.

“In 25 years, I don’t think I’ve ever actually encountered a silencer before that,” Griffin told “Dateline.”

Surveillance footage released by the NYPD shows the suspect in the shooting death of United Healthcare CEO Brian Thompson on Dec. 4, 2024. (NYPD Crimestoppers)

Surveillance video shows a hooded man approach Thompson from behind and open fire with a handgun.

NYPD detectives were able to trace the suspect’s movements back from the crime scene to a hostel where they found surveillance video where he pulled his mask down and smiled at the clerk.

Luigi Mangione smiling and talking to a hostel employee on surveillance footage

Surveillance footage shows Luigi Mangione, the suspected gunman in UnitedHealthcare CEO Brian Thompson’s murder, flirting with a hostel employee before the Dec. 4 shooting. (Crime Stoppers)

That image circulated widely, leading customers and workers at a Pennsylvania McDonald’s to call 911 five days later when Mangione was eating breakfast at a corner table.

He was arrested there, and searches of his bag allegedly turned up the suspected murder weapon and a 3D-printed suppressor.

“You go back to the theory that these guys think they can get away with anything,” Diaz said. “Somebody recognized him…In New York he’s one among millions — where he went, he stood out as an outsider.”

Mangione is due back in both courthouses next week.

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