Actually, I think you’re on to something there. I tend to think the house was the target. Someone earlier astutely referred to it as a “fishbowl.”
The occupants who were killed were sharing a room with someone that night, and those who were spared were not. My own opinion is that the bedrooms with the victims were unlocked, while the bedrooms with the survivors were locked prior to the attack. Possibly, the companions in the rooms were the last to enter and did not lock the doors, even if that might have been a regular practice for the primary occupants.
Like some others, I wonder whether this murderer had entered the house on other occasions unbeknownst to the occupants. And on this night, some of the bedroom doors were unlocked.
MOO