He's been on the road promoting his film for about a year now, but that doesn't mean Joshua Oppenheimer is any less passionate about his Oscar-nominated documentary, "The Act of Killing." Ask the Texas-born, Denmark-residing director a question about his work and it may be a good 10 minutes before he comes up for air.

"The Act of Killing" is a one-of-a-kind film, in which Oppenheimer engages with former death squad vigilantes responsible for mass killings (an "anti-communist purge") in Indonesia between 1965-66 and encourages them to recreate their experiences on a film within the film. Both films are centered around one vigilante in particular — Anwar Congo, a flashy, former street tough responsible for up to 1,000 killings. He was the 41st killer Oppenheimer had interviewed, but the first to show any hint of feeling troubled by what he had done.

Surely it must have been difficult, I ask Oppenheimer, to gain the trust of men like Congo and work with them over an extended period of time — and in some sense, to befriend them — while knowing what they had done? "I don't know how to make an honest film about another human being without being close to them," states the director. "People think documentarians should be objective, but I think in fact you need to be close, and it's impossible to be close and objective. It's the nature of human relationships. That made it harder."