The Taurus Model 85 handgun was one of 23 firearms stolen from a store in Perry, Ga., and one of nine to have so far made their way into New York City, Boyce said during a Monday press conference at One Police Plaza.
Police had no further details about whether the other weapons had been involved in shootings as well.
Investigators had been seeking the weapon since it was used in Saturday's shooting of Officer Brian Moore near 212th Street and 104th Road in Queens, police said. The handgun was found Monday morning tucked near a family's grill in a backyards near the crime scene, police said. It had three spent rounds, Boyce said.
Demetrius Blackwell, 35, used the weapon to shoot 25-year-old Moore, a 5-year veteran of the NYPD, in the head on Saturday afternoon, police said. Moore was pronounced dead at Jamaica Hospital on Monday afternoon, police said.
Moore and his partner were in an unmarked police car around 6:15 p.m. Saturday when they drove up beside Blackwell after growing suspicious that he had a gun in his waistband. When they confronted him, Blackwell, who had a long rap sheet including for weapons possession, drew the revolver and fired at them, police said. Moore's partner was not hit, officials said.
Two witnesses said they saw Blackwell running with a firearm and multiple other onlookers said they saw him running through back yards, police said. At one point, Blackwell changed his clothes in an effort to elude capture, Boyce said.
Blackwell was arrested soon after the shooting, hiding out in a home near the scene, police said. He was charged with attempted murder, attempted assault on a police officer, assault and criminal possession of a weapon, police said. On Monday, prosecutors elevated charges to murder after Moore died.
Blackwell's multiple arrests date back to 1995 for crimes including assault, robbery and weapons possession, police said. According to prison records, he was convicted of attempted murder after shooting at a car in July 2000. During the five years he was incarcerated, Blackwell was disciplined 18 times for violations including assault on staffers and assault on an inmate, records show.
He was released in August 2005, but returned to prison in March 2007 for another year-long stretch after violating his parole, records show.
"Our city is in mourning. Our hearts are heavy...We lost one of the best amongst us," Mayor Bill de Blasio said at the press conference. "[He was] just 25 years of age, a courageous young man."