Ummm... am I the only one who thinks David is guilty too?
I just watched this movie and came away incredibly incredulous at David's behavior as all of the sick revelations came forward. The way he so vigorously defends his dad and ridicules his mom, not to mention his general animosity and almost paranoia, tell me that he has something to hide as well.
I believe that whatever perverted things the dad was up to, he didn't just do them and then forget about them. I am convinced he had pictures and videos of his victims, and he is just ridiculously lucky that the police didn't find them during their initial raid. I mean look at the obsession both he and his family (especially David) had for recording everything.
If Jesse got involved, you'd have to be stupid not to think that the dad looped in (or tried to loop in) his other kids as well. Jesse was obviously interested in getting directly involved. David may not have done any of the abuse himself, thus the kids didn't implicate him, but I just got this really creepy feeling from him. His working as a clown and obviously being interested in children doesn't inherently make him a pedophile, but when you combine that with what was going on in the house where he lived, I bet he had free access to watch whatever videos they made of the abuse.
The way he treats his mom, and gets incredibly agitated at everyone and everything, is irrational. Unless you look at him and think that he was also terrified of being caught. Especially when he makes a video diary worried that the cops will get their hands on it (what other reason would the cops have for seizing his private video diary??)
Did his dad abuse him? Yeah, no doubt. Did it screw him up emotionally and developmentally? I'm sure. But I can't believe that no one else has suggested that he must have had some knowledge and/or involvement of his father's illegal activities...