Her mother could have been the one who scared him off. When he heard her drive up, he could have quietly let himself out the back door and waited until she entered the house to leave the yard.
This could have been done by a neighbor who was on foot. It could have been someone she knew who stopped by late after the party she attended (could have even been someone who was at the party), she let him in and found out what his motives were after he'd been there for awhile. He could have ordered her to unclothe and get into bed after she refused his advances and he then went into a total rage, found a hammer and a knife and tore into her.
I think the person was on foot. No one in the neighborhood saw or heard a car that I've read about. If we knew the actual time of death (previous night or that morning) it might give us a clue. If it was a neighbor, it would have to have been someone single or whose wife was out of town or who quietly slipped out of the house while his family was asleep and got back in before the awakened. I think the reason the backdoor was not locked was because that is where the killer exited although he may have been let in through the front door. Although with the credit card used for gas, he could have left his car a few blocks from the house and walked there. It gives me the chills just thinking about it.
