A gunman who has terrorized a Washington neighborhood with drive-by shootings struck again, killing a man on a city street after midnight, police said. The unidentified man apparently was the seventh victim of the killer, who has slain two people and injured five others. Police believe one gunman is responsible for the shootings in the Columbia Heights and Mt. Pleasant neighborhoods in Northwest Washington, about three miles from the White House. The shooting spree began Feb. 23. In most of the shootings, the man has pulled up alongside pedestrians walking alone, rolled down a window, and fired a shotgun.