WHITE PLAINS, N.Y. (AP) — Authorities are investigating four police officers involved in the fatal shooting of an off-duty policeman who was gunned down as he tried to stop an assault.

Mount Vernon officer Christopher Ridley was not in uniform Friday when he witnessed a violent assault in nearby White Plains and rushed to break up the fight, authorities said. Witnesses told reporters that Westchester County officers ordered Ridley to drop his gun, then shot the 23-year-old when he didn't immediately comply.

The shooting in downtown White Plains stoked racial tensions in the suburb about 25 miles from midtown Manhattan. Ridley was black; two of the officers involved in the shooting are Hispanic, one is black and one is white.