IMO/MOO
This makes me think of the Lauren Giddings murder. I picture a Stephen McDaniel sort of person, not in looks, more so attitude.
Example: McDaniel was known to the victim peripherally, odd incel type, peeped on her, snuck into her apartment and stole underwear...that kind of perv. He planned to SA her, but was unable to because she fought back.
In a house full of girls, it is hard to say which, but I do have a feeling one was the main target.
There appears to be no evidence of sexual assault, but that doesn't mean the crime wasn't sexually motivated.
Also, not sure this is a 'good theory', but figured I would toss in what is rattling around in my head.
Sidenote: I have read/watched many true crime retellings and it seems common for people to not really register what they are seeing right away. Like people thinking they found a mannequin, when in reality it is a body.
Those roommates were in their home, their safety bubble, invincible at that age anyway. Even though maybe they saw something that would be obvious to a bystander, maybe their brains wouldn't quite accept it right away.
Your first thought might not be 'I guess someone broke in and murdered my 4 friends while we slept a floor below'.
It is a terrifying thought and I feel for them.