I'd bet the rent it's not Hoodie Guy - nor the ex, nor the person(s) who gave K and M a ride, nor anyone they met at the bar that night. IMHO, this attack was planned days or weeks ahead by a psychopathic killer. Somebody had been watching that house and its residents. I've been wrong before, but I am sticking to my intuition on this one. JMHO.
I don’t think it is the hoodie guy, either. There are people who behave impulsively, this is how it looked to me, but any killing takes some planning.
This is exactly what I was thinking about when I was reading your post. To have an argument at a frat party, stealthily escape, go home, get prepared, walk out in such a way that no one sees you, while probably still drunk, and kill, is unusual. What if the attack was the result of another quarrel, much earlier, and was planned? It just takes a certain character who can both enjoy destroying his enemies and also, create enough detachment from them.
As of today, I am not sure who was the target. It might be more complex and in the past. The attacker could be older. One might need to go to earlier time, to kids’ high schools, and see if a classmate of more likely, a parent could bear some grudge. I am absolutely unaware who is the collateral victim, either. Chances are, the killer got his victim. JMO.
And if Kaylee spoke about a stalker, she might have intuitively felt that someone was observing the house. I would not discredit it. JMO.