A thrill kill is probably the closest I would describe my theory as - at this stage, and considering the very little information we as the public have been provided.
I posted a few threads back that it’s my opinion that the house/occupants were targeted due to who they were/who they represented, that being young, attractive, popular college kids. The house IMO was likely somewhere he had been before (likely for a party) meaning he had an idea of the layout, knew the occupants or at least the type of occupants and saw it as a good place to scope out in the lead up.
My thought is, is this a person who at some point was rejected by the college scene? Maybe they attended for a short amount of time before dropping out due to not fitting in. I wonder if after dropping out, he (I’m assuming male in this case IMO) somehow found his way back into the scene and even felt he was accepted by the same popular kids (non specific person/s here, just talking popular college kids in general) who once shunned him. That could be due to him being a little older and having access and the ability to supply illegal items (drugs, alcohol if underage, that type of thing). IMO there was still a trigger that unleashed the years of pent up emotions due to being rejected and an outsider and in my opinion that could’ve been something such as him finally feeling confident and accepted enough to make a move on one of these college girls (not necessarily one of the victims or even someone in their circle) only to find himself rejected once again and realising he was being used all along. A possible trigger like this may have cemented the idea and belief to him that he’s had all along - that ‘popular’ kids are selfish, self-centred, nasty, etc. I’m sure his list could go on.
IMO it wasn’t just the feelings of rejection and a potential trigger that caused him to carry out such a horrific crime. I believe he has always had dark, underlying fantasies and been a bit ‘odd’ to others and this has all come together at the right (or wrong, really) time for him to act on both his urges and his beliefs.
My above theory is also why IMO there isn’t another crime committed by this individual for us to be able to compare it to. I think it was their first, and yes, what a first it would be if that turns out to be true, but stranger things have happened… they always have and they always will!
Editing to say: As for a possible sexual aspect to this crime, I believe there was definitely a sexual component though not in the traditional sense our minds may all first go to (sexual assault). IMO the act of the stabbing was the sexual element of this crime - the knife was chosen due to the up close encounter the weapon provided him with. He ‘got off’ on the killing itself, rather than sexually assaulting a victim/s. IMO he never had an intention of committing a sexual crime as it’s not his M.O.
All my own personal opinion based on what we know/don’t know so far.