First, this is nothing new. Bin Laden has always denied involvement. The only time he acknowledged being responsible, was in some supposed sham video that was "found" in Afghanistan, and claimed by the CIA as some sort of smoking gun proving he did it.
Second, while I certainly have never seen a solid piece of evidence proving that he was involved... Him saying he wasn't involved isn't exactly proof of innocence either. He is after all a crazy bastard who thinks it's perfectly ok to murder people because of the country they were born in.