IMO he may have become enchanted online and then made contact. Or maybe he saw her IRL first through incidental contact, found out her name, and went to SM. I'd bet money he stalked her on SM and the fantasy began, whoever 'she' was. KG had a huge following (60K on TT and half that on IG). Even if KG was not his target, one of the other young women in the house and on her SM may have caught his eye. I suspect from there, he was close enough to make peripheral contact.
I also think he is creepy when you get to know him at all, but can look pretty normal on the surface. Someone knows his cold side; someone knows his explosive rage. I think he's got tech skills, and I think he's super control organized. I think he did late night visits or maybe during the day while they were away.
I base this mostly on intuition, but sadly, also from experience. When one of these obsessive guys decides you're the one, it is not reality-based. A threat-assessment trainer explained to me that oftentimes when they interview the attacker, he'll have fabricated an entire relationship and then when reality hits (she gets a new boyfriend, something that's taking her away, real life rejection, etc.), the reaction is as extreme as the fantasy. And the woman will have absolutely no idea that he's obsessed this way. I think that's what happened here, but on steroids. If you've never had to deal with it, it's hard to explain and 'prove', but it's real, and it is awful to deal with it.
Anyway, I think it was something like this where he was very obsessive and when he realized he couldn't have her, potentially coupled with some other trigger in his life, he started planning. I don't think he just decided at 2:30 a.m. to get in the car and drive. I think he was getting in the car at that time and driving because it was time. And I think that there were 3 incidental murders and 1 focused one. And I suspect there was some freak show to it.
This is all JMO, of course, and I know nothing more than anyone else here. Not as much as many. But this seems very well planned, and these were beautiful young women who did nothing wrong. So I think it takes that kind of psychopath to do something like this. JMO.