Two police officers prepared to enter the pitch-black eighth-floor stairwell of a building in a Brooklyn housing project, one of them with his sidearm drawn. At the same time, a man and his girlfriend, frustrated by a long wait for an elevator, entered the seventh-floor stairwell, 14 steps below. In the darkness, a shot rang out from the officer’s gun, and the 28-year-old man below was struck in the chest and, soon after, fell dead.
The shooting, at 11:15 p.m. on Thursday, invited immediate comparison to the fatal shooting of an unarmed man in Ferguson, Mo. But 12 hours later, just after noon on Friday, the New York police commissioner, William J. Bratton, announced that the shooting was accidental and that the victim, Akai Gurley, had done nothing to provoke a confrontation with the officers.
Indeed, as the investigation continued into Friday night, a leading theory described an instance of simple, yet tragic, clumsiness on the part of the officer. Mr. Gurley was not armed, the police said.
The episode promised to bring scrutiny to a longtime police practice of officers drawing their weapons when patrolling stairwells in housing projects.
The shooting occurred in the Louis H. Pink Houses in the East New York neighborhood. The housing project had been the scene of a recent spate of crimes — there have been two robberies and four assaults in the development in the past month, two homicides in the past year, and a shooting in a nearby lobby last Saturday, Mr. Bratton said.
Additional officers, many new to the Police Department, were assigned to patrol the buildings, including the two officers in the stairwell on Thursday night, who were working an overtime tour.
Having just inspected the roof, the officers prepared to conduct what is known as a vertical patrol, an inspection of a building’s staircases, which tend to be a magnet for criminal activity or quality-of-life nuisances.
Both officers took out their flashlights, and one, Peter Liang, 27, a probationary officer with less than 18 months on the job, drew his sidearm, a 9-millimeter semiautomatic.
Officer Liang is left-handed, and he tried to turn the knob of the door that opens to the stairwell with that hand while also holding the gun, according to a high-ranking police official who was familiar with the investigation and who emphasized that the account could change.
It appears that in turning the knob and pushing the door open, Officer Liang rotated the barrel of the gun down and accidentally fired, the official said. He and the other officer both jumped back into the hallway, and Officer Liang shouted something to the effect that he had accidentally fired his weapon, the official said.
Mr. Gurley had spent the past hours getting his hair braided at a friend’s apartment. Neighbors said he had posted photos of himself on an online site for models, featuring his tattoos, his clothing and his muscular frame.
He and his girlfriend, Melissa Butler, waited for an elevator on the seventh floor, but it never came, so they opened the door to the dark stairwell instead. An instant later, the shot was fired. Mr. Gurley and Ms. Butler were probably unaware that the shot came from a police officer’s gun.
“The cop didn’t present himself, he just shot him in the chest,” Janice Butler, Ms. Butler’s sister, said. “They didn’t see their face or nothing.”
Mr. Gurley made it two flights down, to the fifth floor, where he collapsed. Melissa Butler called 911 from a lower floor, the official said.