I wonder about targeting and if there is a primary and secondary target. Specifically one person could be the primary but the entire friend group could be the secondary. Then something happened that stopped the killer from going the other 2 roommates. The psychology of targeting the friend group could be jealousy (they are close to the target), revenge (they stood in the killers way or he knew it would hurt the target even more if friends were dead). Or perhaps targeting the friends was just a part of the overall appetite for death. It is all disturbing and I seriously hope they had minimal awareness of what was going on
I feel like it's more likely that this was targeted killings by an unknown pathological stalker, who was perhaps obsessed with KG via social media (it was public), knew that she was coming back into town for the weekend, and seized on his fantasy/compulsion. The elevated and 'hidden' parking lot behind the house would be ideal to sit and wait and watch. From that vantage point, I think he could have seen the second and third floor activities (and when the lights went out on each), so therefore knew that he would have to kill others just to get to her (which probably thrilled him - ugh). He would likely not have known about nor seen the first floor rooms/any lights therein.
Probably not his first time. Or if it was, probably not his last.
My opinion.