Considering he actually lived in Cambodia during that whole massacre he probably had a lot of experience to draw on.
Acting isn't all that easy...otherwise why are there so many bad actors?
So that suddenly makes him an Oscar-worthy actor??
There aren't so many bad actors. There's poor casting, poor role choosing, there's personal opinion and that's about it. An actor is fine if in the right role. Can't expect anyone to be Daniel Day-Lewis but what other profession has people with no experience, children and mentally handicapped people ranked so highly? When 8 year olds can win Oscars it isn't exactly rocket surgery.