Just wanted to share some thoughts on idea that this is not targeted because four people were killed. I think it is still very likely targeted and have not heard an argument to exclude it.
If killer, be it a person with prior familiarity with home or not, had a specific target, things still could have gone the way they did. they may have entered the home, entered the room they thought their tarte was in, and found out only after killing each one, that it was not their target, until they finally did get their target, killed them, and then left. The order in which the attacks were committed would likely be determined by a) blood trials (which blood trial from dripping knife had one arsons blood, or two, three or four persons blood b) stab wounds or bedding having one, two, three or four persons blood in them.
And yes a person familiar with house could still get rooms wrong. When I was in undergrad for soph, junior and senior year I lived in a five bedroom house with five of us. Each summer one or two would leave due to graduating, moving in with a boy/girl friend, getting own place etc. And we always switched rooms with who ever had longest tenancy in the place having seniority in picking bigger room. so someone who had been to Idaho house, even several times, could have gotten two rooms wrong, sneaking in, stabbing and then seeing wrong person, moving onto next room, and next, finally getting it right their intended target -- and then leaving.
The order is important because the last person killed is likely the primary target sand thus their circle, boyfriends, dating partners, potential stalkers, would be important persons of interest
Also it could be targeted even if their was one primary victim. If the killer were an ex of one of the three girls, they could be holding grudge on the other two girls who were killed, for real or imagined interference in relationship. I've had friends my partners have resented.
I have not heard what definitely exculpates all prior boyfriends/dating partners. Even the exculpation of one person seems strange, with effusive but weird praise, that half sounds more like a setup scripted by investigators.