Here's my problem with the supposition that Lonzie was dead before his mother went to work:
LL had the OPTION to go to work according to MSM reports. She did not have to show up or lose her job.
WRE was in a hurry to get things done before she got off work,WHY?
They would have had all the time they wanted to hide a crime and come up with a much better story than WRE gave (the stolen car and baby scenario) if she had not gone to work that night.
It just doesn't add up.
He was thinking on his feet. He made a lot of mistakes because he needed to have a plausible story before she got home. If she knew, her help hiding the crime would have made a lot more sense than her going to work. It would make more sense for her to stay with the 5 year old, keep her sleeping and unaware than for him to run around with a 5 year old, trying to cover up the mess he made.