I'm not sure I've seen this standard applied to anyone under these circumstances. They sound devastated on the phone. In mourning. LE probably looked at their hands for injuries, their clothing, assessed the scene, their rooms and made the right call IMOWe may not like it being applied in this case, but in general, it's actually a pretty big deal that officers arrived on the scene of a homicide and did not separate the witnesses before they were questioned. The theory is, they could influence each other. At that time, officers had no idea what was going on, so separating them should have been one of the first steps once it was clear this was a homicide investigation. It's the same reason we don't allow witnesses in the courtroom until they've testified.
MOO.
Even the suspicious husband gets a "come down to the station tonight" or "come down to the station tomorrow morning"
As far as the other students, they weren't there when the crime took place. If LE tried to 'clear crime scenes' by separating everyone who is in and around it hours and hours after the fact that would be a complete waste of resources and time.
If caveats exist, this is the time.
MOO