I agree, the police have an idea who did this as well.
Also, I find it strange that the roommates who survived, called their friends after finding “an unconscious roommate.”
We know from the parents of the victim, that the crime scene was “messy.” This leads me to believe we are either being kept in the dark, or the roommates are lying. They would have to have seen all the blood and carnage to just see one victim, and they decided to call friends instead of calling the police or for real help. Not buying this. Roommates no more or we don’t really know what they told police.
No way the killer was a stranger, unless he is the luckiest person alive. There were to many victims and variables, like the dog. The killer knew the dog wasn’t an issue and that it wouldn’t make noise or try to defend anyone. The killer could have even been seen in the house and the victims wouldn’t have had a second thought. The victims know who he is and wouldn’t have reacted if they did see him.