I met soldiers coming back from war and I was impressed by their description of PTSD, all the symptoms: the outburst of violence, the impossibility to cope with reality anymore, all that stuff.
I had experience with PTSD myself; probably that's why I felt so close to the soldiers and the testimony. Also, because I had experienced this myself, I wanted to make a really physical and carnal film.
Since PTSD is being exposed to death and the death of someone close, I felt really close to [the soldiers].
It's the doubt that is really a major ingredient of the paranoid thriller.