The filmmaker Jarecki is clearly not biased and out to try get him though- he even seems to have developed a kind of rapport with Durst and he's hesitant to call him out for the handwriting at the end, he doesn't want it to come across as a 'cold' attack. He just can't deny the blatant evidence right in front of him! Without all of his money Durst would have been proven guilty a looooong time ago.
While the evidence overwhelmingly points to him being guilty, burping or facial gestures or whatever aren't proof of anything. If I were guilty or not I would probably have a lot of anxiety in that type of situation and I'd most likely be fidgety.
Out to get him? Hold up a minute--Durst is the one who contacted the filmmakers himself and said he'd like to tell his side of the story after he saw Jarecki's only (to date) non-documentary film ALL GOOD THINGS, a fictionalized story of the Durst case. So nobody made him do jack. He put himself up there to be examined,plain and simple. Apparently his arrogance overrode his common sense, and he figured that no one would really question his views on events in his cases. He figured wrong, obviously, which is why he's been arrested.
Lol the film crew wasn't a bunch of valiant truth finders. They were trying to bust him. Durst was under the impression he was going to tell his side of the story and that Jarecki was on his side. Jarecki kind of betrayed that trust and to me a lot of that is exploitation of a guy trying to make it big with a documentary.