The genre portrayed in 'The Act Of Killing' is a hard one to estimate, as in my opinion it has more than one. I think that the main genre of this documentary is observational however it also contains a lot of performative elements. The reason i think it is observational is that there was not much sound or music included in this documentary. The film maker may have used this as a tool to make it more mature and serious as the subject that the documentary is on is quite a serious one, however as it was more about gaining information about how they killed the communists which is why it was more performative as there was re-enactment and interviews with the people who actually committed the killings.
The relationship between the documentary and reality is an interesting concept to think about