Luigi Mangione is facing a second-degree murder charge in New York City in connection with the brazen shooting of UnitedHealthcare CEO Brian Thompson in Midtown Manhattan as new details emerge about the suspect and a potential motive, according to police.

"We do have a lot of evidence in this case," NYPD Commissioner Jessica Tisch told ABC News' "Good Morning America" on Tuesday.

"When he was found he was in possession of the same New Jersey fake identification that was used at the hostel" on New York's Upper West Side before Thompson was gunned down on Dec. 4, she said.

The gun 26-year-old Mangione was allegedly found with on Monday "looks very similar" to the gun used in the murder, "with a similar suppressor," Tisch said. "So there’s a lot of reasons that we feel very strongly that he is the person of interest."

Officers allegedly found a black 3D printed pistol and a black silencer, which was also 3D printed, according to the criminal complaint filed in Blair County, Pennsylvania.

"The pistol had one loaded Glock magazine with six nine-millimeter full metal jack rounds. There was also one loose nine-millimeter hollow point round," according to the complaint.

NYPD Chief of Detective Joe Kenny described the weapon as a "ghost gun," meaning it had no serial number and was untraceable.

Mangione, who was arrested in Altoona, Pennsylvania, on Monday, remains in the custody of the Pennsylvania Department of Corrections pending his extradition to New York.

The NYPD was "thrilled" to get the call from Altoona police that they had a person of interest in custody, Tisch told "GMA."

Kenny said "the key to this case" was releasing the photo of the suspect's face to the media and the public.

"That picture reached Pennsylvania," where he was recognized at a McDonald’s on Monday morning, he said.

"We are grateful as a city to that person," Tisch said.

"We had collected early in the investigation some forensic evidence, some DNA evidence, some fingerprints, so we were very confident that we were ultimately going to get to the right person," Tisch added.

When Mangione was arrested he had several handwritten pages on him that appeared to express a "disdain for corporate America" and indicated "he’s frustrated with the health care system in the United States," Kenny said.

"Specifically, he states how we are the No. 1 most expensive health care system in the world, yet the life expectancy of an American is ranked 42 in the world," Kenny said.

Whether Mangione has a personal connection to UnitedHealthcare is unknown, Tisch said, but the writings mention UnitedHealthcare by name, law enforcement sources told ABC News.

The sources described the handwriting as sloppy and included these quotes: "These parasites had it coming" and "I do apologize for any strife and trauma, but it had to be done."

Police are now looking at Mangione’s travel at various points across the United States and out of the county within the past year, the sources said.

Mangione, a Maryland native and Ivy League graduate, was also charged in New York with possession of a loaded firearm, possession of a forged instrument and criminal possession of a weapon.

He was charged with five crimes in Pennsylvania, including carrying a gun without a license, forgery, falsely identifying himself to authorities and possessing "instruments of crime," according to the criminal complaint.

This is a developing story. Please check back for updates.