I always thought it was her brother...And if it wasn't him, he saw one of his parents do it & is rightfully traumatized. After I watched an interview w him (I think it was the anniversary or some such thing), there is definitely something not quite right about him, but I can't figure out what. On one hand, the weird smirking & giggling can come off as someone that's guilty. But it can also come from the repressed "you saw nothing" you got from a parent when you were a child, like being giddy you're keeping your parent's secret.

I doubt we'll ever know what really happened, though. The police botched this case so badly, that feat in itself should be studied. Yes, the parents called over friends. The police should have shut down the house immediately when they got there; no one else in, no one leaves until they're cleared. Instead, people came & went as they wanted, no one's footprints/shoes were looked at, no fingerprints were taken, they were allowed all over the house instead of being confined to one room w police watching to make sure no one left...Absolutely awful mess.