A rookie cop working the most dangerous beat in the city killed a man in an unlit housing-project stairwell in Brooklyn — firing off an “accidental” shot that hit a young father in the chest, authorities said Friday. “It was a pitch-black hallway,” Police Commissioner Bill Bratton said of the Thursday-night shooting at East New York’s Louis Pink Houses. “The deceased is a total innocent.” -snip- With his gun in his left hand and a flashlight in his right, Liang entered the stairwell at the same time Akai Gurley, 28, and his girlfriend, Melissa Butler, walked into the same stairwell...