That's another point --- Why mow the lawn that day if he knows he's about to commit a crime so heinous that he will never again want to step foot in the house? Surely he would know that he wouldn't be staying there again following the murder, so why bother cutting the grass at all? I think it's important to look at the actions of people not just after a crime but also before.
Maybe he needed a reason to stay home instead of leaving early for his meeting? He could have left earlier and gone the entire way, settled in and been on time for the meeting.