Fairfax County's police chief said yesterday that one of his officers accidentally shot and killed an optometrist outside the unarmed man's townhouse Tuesday night as an undercover detective was about to arrest him on suspicion of gambling on sports. Police had been secretly making bets with Salvatore J. Culosi Jr., 37, since October as part of a gambling investigation, according to court records. They planned to search his home in the Fair Oaks area, just off Lee Highway, shortly after 9:30 p.m Culosi came out of his townhouse on Cavalier Landing Court about 9:35 p.m. and was standing next to...