As of right now there is no evidence to say he was or wasn't....we are here to discuss thoughts and theories of known facts. Stating that he wasn't involved isn't a known fact....it is an opinion.
He was a pretty sight kid. I doubt he would have the power to kill his sister. The most likely scenario when one child injures another is to rush the victim to the hospital, where JBR could have been saved. Instead, we are suggesting that the parents finished the job and half-staged a kidnapping?
I think those parents have isolated their son till this point for fear he would go off script and interfere with the phony scenario they swear by. He was heard asking questions on the 911 tapes like he didn't understand what was going on. Telling him to shut up, stay in his room and stick to that story was the best way to keep his playing downstairs after lights out to ruin their story of an intruder.