Otto I think that is all correct, except I'd disagree that the idea is that only a father would leave the child alive as a witness. To me, the idea is the universe of people who would not only leave the child alive, but also (if you believe it happened) cleaned her up, and cleaned him/herself is limited, and JY is in it. I do agree it can't be known that someone else wouldn't have acted the same, but there is logic in thinking JY would be someone who would do those three things. Its a part of the picture, but not meant to say this proves it, by itself.
However, the PT may hard sell it as you say. We'll know tomorrow!