Luigi Mangione, 26, was arrested at a McDonald's in Pennsylvania on Monday.
As Luigi Mangione was handcuffed and placed under arrest in Pennsylvania on Monday, police searched the backpack he'd been carrying and found what they described as a loaded 3D-printed firearm, a suppressor and a single loose bullet.
"Officers located a black 3D-printed pistol and a black silencer," wrote Tyler Frye and Joseph Detwiler, members of the Altoona Police Department, in a criminal complaint. They described the weapon as having "a metal slide and a plastic handle with a metal threaded barrel."
"The pistol had one loaded Glock magazine with six nine-millimeter full metal jacket rounds. There was also one loose nine-millimeter hollow point round," the officers wrote. "The silencer was also 3D printed."
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Mangione, whom New York officials charged with second-degree murder in connection with last week's "brazen" killing of a CEO in Manhattan, was first arrested in Altoona on Monday on charges that included a felony related to the gun, according to the criminal complaint.
Mangione faces a third-degree felony charge for allegedly carrying a concealed firearm without a license, according to the complaint. He also faces a misdemeanor charge for allegedly "possessing instruments of crime," along with three additional Pennsylvania charges related to allegedly lying to police about his identity.
The weapon will now undergo ballistic testing, New York Police Department Chief Joseph Kenny said on Monday. He said information about the weapon had begun coming in from Altoona police and that it appeared to be a "ghost gun," meaning it had no serial number and was untraceable.
"May have been made on a 3D printer, with the capability of firing a 9 mm round," Kenny said. "Obviously that will come out during our ballistics testing."
Kenny said it was too early in the investigation to detail whether the gun could have been made by the suspect or purchased. But the gun and 3D-printed suppressor were "consistent with the weapon used in the murder," NYPD Commissioner Jessica Tisch said following Mangione's arrest on Monday.
Law enforcement had looked closely last week at what weapon may have been used in the killing, officials said, as the gun's operation appeared to be somewhat unique in its operation.
Detectives had studied a surveillance video that showed the fatal shooting, saying it appeared to show "that the gun malfunctions, as he clears the jam and begins to fire again," Kenny had said last week.
Police sources told ABC News on Thursday that those apparent malfunctions may point to the weapons being a B&T Station Six, a type of pistol with an integrated silencer that's known in Great Britain as a Welrod pistol.
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Such firearms have long barrels that enables them to fire 9 mm bullets with a nearly silent shot, officials said. They also require manually cycling ammunition from the magazine.
But New York Mayor Eric Adams said untraceable weapons were "extremely dangerous," adding that there needed to be a federal "clamp down on the availability of ghost guns."
ABC New's Aaron Katersky, Peter Charalambous, Mark Crudele and Josh Margolin contributed to this report.