The revelation of the presence of the two unharmed roommates did seem like a bombshell. However, based on what was said at the press conference, it doesn't seem like the police consider them to be suspects or persons of interest. It's conceivable that they slept through the murders and woke up late to a horrible scene.
The revelation about the roommates probably explains why the police first described the killing as "targeted" (because 4 people were killed and 2 were left unharmed). But it's conceivable that the unharmed girls were just overlooked by the killer.
So as surprising as the new fact about the roommates is, we still don't know whether the killer was known to the victims or unknown. As I stated in a post earlier today, the more time that goes by without the police naming a suspect or a person of interest, the more I think this might be a case of a random killer, perhaps a serial killer. If it were someone known to the killers, then it seems like the police should have made some progress by now. But if it were a random/serial killer who disappeared into the night and fled far away then I can understand how the police are having such a hard time making progress.
As surprising as it was to hear about the presence of the two surviving roommates, I was left with the feeling of we got nothin'.