Picture this then. Westerfield is the "extra man", and he gets sexually worked up, but he isn't allowed to play in their Raindeer Games. I mean, he is REALLY aroused and they lock him out of the garage where Brenda and Damon and the others are drinking, doing drugs and each other. Got the picture? OK...so then the aroused Westerfield goes up stairs and abducts the child. The rest is history.
Point? Aren't the parents culpable for inviting that EXTRA man over? Remember, they weren't exactly sitting around a table, playing a hand of Bridge.
sw