A Brooklyn cop responding to a robbery mortally wounded an armed man with a single shot to the chest, police said Friday. Only after Duane Browne died did investigators learn that he had been racing to help his drug-dealing half-brother when he ran into the cops, police said. Browne was apparently unaware that his sibling, Dale Ogarro, had already fled the house through a back door and was talking to officers. And Ogarro didn’t tell the police...