To follow-up on on of my earlier posts, I still have absolutely no strong opinions on who exactly could have done this, but have a lot of theories. Some points:
1) The killer could have been solo, or there could have possibly been 2 people. But, I lean more towards a solo killer. It would have been a lot easier for one person to have done this quickly, left the house, and then subsequently left the area without attracting any/a lot of attention - than for 2 people to have done this. It's also a lot easier for one person to do a crime like this & keep their mouth shut - than for 2 people to keep quiet about this.
2) I lean towards the killer being male, but am open to the possibility of a female. Whether male or female, I strongly suspect the person was physically powerful/strong.
3) I don't believe the killer/killers knew about the 2 surviving victims on the bottom floor. Or, if they did know about the 2 survivors, they were rushed and didn't have time for them. Or, maybe they tried the door & since it was locked, didn't want to take the time/energy to break down the door (which would cause a lot of noise)/pick the lock and risk the 2 waking up & being able to fight back, etc. But, I'm leaning toward the idea that they were unaware these 2 were in the house.
4) As far as who did this & what the motive was?! I have no single, definitive theory. It's possible that this was:
a) Someone known to one or more of the 4 in the group, who was enraged about a real or perceived slight/insult/rejection/etc. Maybe they were fuming about this for a long time, until they finally exploded.
b) Going along with the above: The killer could have been a stalker of one (or more) of the girls, that escalated to murder.
c) Or, it's possible they were not known to anyone in the group. They could have been a local person/persons in the town/area who were angry/jealous about these attractive young people with seemingly bright futures, and decided to lash out.
d) However, it's also possible this was a beginning?! serial killer/killers who did know who lived in the house but may never have met any of them & didn't have anything against any of them specifically. They may have just decided to assault the 4 just because they are a malicious psychopath/psychopaths.
e) They may have been a local. Or, they may have been a drifter/drifters who was/were passing through town & maybe stayed for a brief period.
In other words, IMHO this could have been anyone.