NYPD Commissioner Jessica Tisch says police have matched a 3D-printed gun allegedly recovered from suspected killer Luigi Mangione to shell casings found outside a New York City Hilton where UnitedHealthcare CEO Brian Thompson was gunned down from behind last week.

"First, we got the gun in question back from Pennsylvania," she told reporters at a news briefing Wednesday. "It's now at the NYPD crime lab. We were able to match that gun to the three shell casings that we found in Midtown at the scene of the homicide."

They also have his fingerprints on a snack bar wrapper and a water bottle, she said.

"We were also able at our crime lab to match the person of interest’s fingerprints with fingerprints that we found on both the water bottle and the KIND bar near the scene of the homicide in midtown," she added.

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Tisch and NYPD Chief of Detectives Joseph Kenny previously told Fox News they found a burner phone and other physical evidence linked to the suspect which they were checking for prints and DNA evidence.

Altoona police likely fingerprinted Mangione after his arrest in Pennsylvania Monday on fake ID and firearms charges and uploaded them to a law enforcement database the same day, according to Paul Mauro, a former NYPD inspector. 

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From there, investigators in New York could quickly match them with samples recovered in the Big Apple after the murder.

Altoona police said they found a black 3D-printed pistol and a black suppressor when they arrested Mangione.

"The pistol had a metal slide and a plastic handle with a metal threaded barrel," according to court documents. "The pistol had one loaded Glock magazine with six nine-millimeter full metal jacket rounds."

The NYPD previously said it recovered both spent casings and unfired rounds from outside the Hilton hotel, where Thompson was murdered on Wednesday, Dec. 4. The shells had writing on them, according to authorities, including the words "deny," "defend" and "depose."

Those words are similar to the title of a book critical of the health care industry, "Delay, Deny, Defend: Why Insurance Companies Don't Pay Claims and What You Can Do About It." Although Mangione had an active Goodreads account, that particular missive was not on his reading list.

But investigators said they were looking into whether a denied claim played a role in the slaying.

Mangione is being held without bail in a Pennsylvania jail awaiting extradition to New York to face murder and other charges.

His lawyer said in court Tuesday that he planned to fight extradition, potentially delaying his transfer to New York custody by days or weeks.

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He is also facing firearms and other charges in Pennsylvania, where police say they found him with a 3D-printed ghost gun, the same fake ID he used to check into a New York hostel, and $10,000 cash.

Local prosecutors said they planned to move forward with their case but the more serious homicide charges out of state will take precedence.