It is simultaneously the most extraordinary documentary you've seen and also most chilling comment on the depths and banality of human brutality.

It's unlike anything on film: The mass murderers believe they are showing off their exploits to an appreciative audience, demonstrating to the filmmakers what they did. They go so far as to end up acting out a surreal fantasy, complete with sets and costumes, which cannot be described. But this is a serious documentary about a horrible event; it's not parody or satire. Somehow, the perpetrators of the killings reveal themselves.

http://www.nytimes.com/2013/07/19/movies/act-of-killing-re-e...

I came here to say this too. I think it's the most shocking film I've ever seen, and it achieves it without showing a drop of blood. In fact, it's almost impossible to explain how it does achieve it - you just have to watch it. It's truly surreal in places.

Thanks for recommending this. I saw this in the cinema and it was the only time I've ever felt the need to walk out of a film, it's that powerful/horrific.

I highly recommend the follow up "The Look of Silence" as well