I think the worst video, which said/implied the murders would be the next day, was probably not seen by the police.
The worst video was apparently the last one, which he posted 10 minutes before he started shooting, and after he’d killed the three roommates. Given that the therapist, after seeing it, called the Sheriff’s department, it’s safe to say that it indicated an escalation of his prior fantasies. Neither the parents, the therapist, nor the Sheriff’s Department saw that one before the incident was over.