A tense ethical showdown with the racing pulse of a thriller, “September 5” revisits the day in 1972 when the Munich Olympics became a very different kind of international spectacle. Before dawn that morning, while many of the world’s elite athletes were still sleeping in the Olympic Village or drunkenly heading for bed, eight heavily armed members of Black September, a militant Palestinian group, easily scrambled over a perimeter fence in the village. They quickly made their way to the building where the Israeli delegation was housed and took 11 of its members hostage, shooting two men, who soon died.