In the house before: Yes, I absolutely agree with you there. May have only been once but when you combine that with the amount of publicly available info on the layout of the home, that's probably all it took.
In the house on the night of the murders before they occurred: No - I have never believed that and would be very surprised if that is the case.
It certainly is a unique house. Three stories. On an slope. Multiple sliding doors. I wonder if any of that played into why the killer chose it in the first place?