I have felt like RH was guilty from the beginning and also suspect LH's involvement, but playing Devil's advocate and thinking about context, I wonder about this statement "Did you say too much?" It sounds bad, really bad. But, if she truly believed this was an accident, than it would be smart to advise RH "not to say too much".
Our family just had a terrible experience of having our son falsely accused of a crime. You'll just have to trust me that it was indeed a false accusation. But there was a series of coincidences that briefly made things look pretty bad for my son. Our first inclination was to just talk to the police, thinking that the truth would prevail and the whole mess would get sorted out. But we had also read online that you should never, ever talk to police if you have been falsely accused of something. We felt very confused, because on TV and often on Websleuths, I know that when someone "lawyers up" they look guilty. But I was reading that in real life you should always lawyer up and zip it--even if you are totally and completely innocent. So, in the end we told the police that our son would not be talking to them. In the end it became very clear that the accusations were false and the DA declined to press charges.
So, I have a new perspective about not talking to the police. But having said that, in this case we are talking about a very extreme situation of the possible murder of a child. In light of that, I can't understand the lack of emotion in what LH said to her husband. Was this the first time seeing him right after being informed that her child was dead? Who would be that lucid and reasonable to be thinking about such things? I just don't get that--I mean I would be screaming, "What happened? What did you do?" and beating him with my fists. Yeah, yeah I know people grieve differently--but I don't believe asking "Well, did you say too much?" fits into the range of normal. I just can't wrap my mind around it. I need context.
But I still believe Rh is guilty based on the very short drive, close proximity to child in car seat, this being RH's normal routine, and the smell in the car. All the other stuff is just curious and bizarre extras for me.