I don't know that he did it deliberately.
But I've followed enough cases here to know that often, the guilty often do things that 'make absolutely no sense' to most of us.
That being said, I can imagine that the person who had the psychological makeup to be able to justify intellectually the craven act baking their child to death to begin freeing themselves of entanglements, would also be a person who would be morbidly curious if the 'hard work' of killing the child was done by lunch time, so he could focus on Act II, The Dramatic Discovery in front of maximum audience.
I also am not sure about the intent aspect. Your explanation about why he would go back if he did intend to kill Cooper is spot on. I couldn't agree more.