I think about how cautious and careful SB has been from day one. He has diverted suspicion away from the parents in almost every interview he's given (or at least he's been so vague that it wasn't clear he ever thought they were involved). Even now, it almost pains him to have to disclose that the parents are suspects. I think that SB does not take such accusations lightly and is very aware of the repercussions. I don't believe for a second that he would make a statement like that without a whole lot of evidence to back it up (as in, enough evidence to prosecute). I feel that Klein's arrival kind of sped things up and that if left to his own devices, that SB may have prolonged naming them suspects. I think SB was just observing everything and hoping/praying for someone to rat someone out, and in the meantime, he played "good cop" so as not to tip them off. Once it was obvious that they were the prime suspects (which became clear after Klein's statements), there really was probably little reason for SB to keep it secret any longer. At some point you just have to cut to the chase, so to speak.
As far as the parents' guilty knowledge, I think that when you look at the individual actions of the parents, there is always a way to explain their actions with some amount of credibility, but when you look at the sum of their actions, it really becomes clear, at least to me, that their collective actions are not indicative of parents who are really trying to find their toddler and/or who really have no idea what happened to him.
MOO.