A rookie cop killed an unarmed, innocent man late Thursday night when his weapon accidentally discharged in a darkened stairwell of a Brooklyn housing project, NYPD Commissioner William Bratton said Friday.

"No dialogue was exchanged" before Officer Peter Liang shot Akai Gurley in the stairwell, where the men crossed paths, Bratton said.

Gurley, a 28-year-old father of a 2-year-old, was unarmed.

"The deceased is totally innocent," Bratton said at a news conference yesterday. "This is a very unfortunate tragedy. It appears that this was an accidental discharge."

Liang, on the job fewer than 18 months, has been put on modified duty and stripped of his badge and gun during an internal investigation of the shooting, which happened inside of the Louis H. Pink Houses of East New York, on Linden Boulevard.

Late Friday, Bratton, Mayor Bill de Blasio and his wife, Chirlane McCray, met with Gurley's family. The family is to appear Saturday in Harlem for the Rev. Al Sharpton's weekly rally.

Just before the shooting, Gurley had been at a girlfriend's seventh-floor apartment in the building. The couple then took the stairs because the elevator was delayed. Liang and his partner were descending from the eighth floor, on "vertical patrol" to combat a crime uptick, including recent robberies, assaults and homicides.

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After the 11:15 p.m. shooting, Liang and his partner left the scene but returned a short time later. Gurley, who police said was hit once in the chest, died at Brookdale University Hospital and Medical Center at 11:55 p.m. The officers went to Jamaica Hospital Medical Center for tinnitus, ringing in the ears.

De Blasio, speaking Friday at an unrelated news conference in the Bronx, said: "On a very human level, we lost a life today -- and I feel that very humanly, as I'm sure all New Yorkers do."

Bratton said Liang had drawn his weapon before encountering Gurley and "will have to give justification why his gun was unholstered."

"We leave that decision as to when to take a firearm out to the discretion of the officers based on what they are encountering or believe they may encounter," Bratton said. "There's not a specific prohibition against taking a firearm out."

Liang's labor union president, Patrick Lynch of the Patrolmen's Benevolent Association, said in a statement that "only time and a thorough investigation will tell us what transpired in this case."

The city's public advocate, Letitia James, said she is "deeply disturbed" by the shooting.

Rep. Hakeem Jeffries (D-Brooklyn) said: "The senseless killing of another unarmed African-American male by the NYPD should shock the conscience of all New Yorkers and the nation. At this point, talk is cheap. The community demands action."

With Matthew Chayes