Some things that have occurred to me that may or may not be helpful: (JMO)
We know the rough timeframe in which the killings took place but not necessarily how long the perp was present at the house. I don’t know (and apologies for this image) - how long it would have taken to stab 4 people to death/incapacitation. If there was little resistance then I imagine this was quite quick - maybe a little longer for those who fought back, but it must have been quick enough to not raise the alarm substantially (especially with possibly two people in each room). There is a chance that the perp then was able to do things to one of the victims, which would explain why LE have stated they think it was targeted (e.g. notes or particular mutilation). They have said the upstairs floors were worse. Alternatively this time could have been used to clean self up a bit (e.g. swap shoes to not leave footprints). I think ultimately this theory depends on what order everything happened in and motive and unfortunately we don’t have that information but it’s a question I hadn’t seen raised - ie whether perp left straight away after “rage” or was more calm and collected and stayed in house for longer after, maybe mistakenly not realising there were two additional roommates.
Secondly - and apologies for bringing it up again but IF that is blood on the outside of the house, is there a chance it could have also permeated the floor of the bedroom / ceiling of the first floor as well? Please correct me if not as I know some discussion on whether it was laminate floor but that could offer another reason to why the roommates were alerted to some danger but possibly didn’t know the full extent and so didn’t leave their locked room / called friends first out of fear for their own safety. Once the friends arrived at the house they confirmed the scene and that’s when LE were called. Again I’m not too sure on this as conscious the report is that they called friends because they “believed one of the second-floor victims had passed out and was not waking up" - which might make more sense with a locked door. If there was a locked door IMO I think this lends itself more to a killer that was calm and collected and not in a fit of rage.
ID - 4 University of Idaho Students Murdered - Moscow # 8