JAKARTA, Indonesia — The American director of the chilling Indonesian documentary “The Act of Killing” has won dozens of awards so far for the film and could add one of the movie industry’s most coveted honors Sunday at the Oscars.

But so far, the director, Joshua Oppenheimer, has not succeeded in accomplishing what he considered a greater goal — jump-starting a debate in Indonesia that will compel the government to finally open a formal inquiry into one of the worst mass murders of the 20th century.

The film, nominated as best documentary, recounts in graphic detail the killings of an estimated 500,000 or more Indonesians during state-sponsored purges of suspected Communists and their sympathizers in 1965 and 1966....