Not someone who usually posts on these sort of things but I had a theory and felt it worth sharing, my apologies if this has already been covered but I haven’t seen it discussed much yet.
So I’ve been trying to rationalize how (1) the killer seemingly left the scene without being caught on camera or by another person, (2) why they chose this house and these girls, and (3) how their clothes must’ve been covered in blood and were able to clean up/dispose of them without being caught. Then it hit me — I think there is a fair chance the crime was committed by someone who lives in the apartment building directly next to/behind the house. It not only answers all of these questions but it would fit most of the possible narratives (outside of an ex) being discussed here: loser incel, stalker, thrill kill, etc.
Here me out: (1) according to google maps the home and the apartment building are 30 ft apart with less than a minute walk between them and the fastest route being through the hill/tree line behind the house. This not only aligns with the already assumed path of entry but would also explain how the killer or his vehicle wasn’t caught on any ring cameras/surveillance footage in the neighborhood — he didn’t drive. (2) The parking lot for the residents of that building backs up directly to the back of the home. You could park a car in that lot and see directly into the third story windows, which happens to be M & K’s bedrooms. Is it possible some loser resident parked there at one point, looked up and noticed these pretty girls laughing in their bedroom through the window and became kind of obsessed with them? Seems like a stretch, but at this point it is a possible explanation for how this could be “targeted” but yet still seemingly random. (3) Most of the apartments in that building are ONE BEDROOM apartments. This explains how he could have been covered in blood and cleaned himself/his clothes without a roommate or anyone noticing. It also fits the profile for some antisocial incel type to live alone. Not that there’s anything wrong with that but in college it’s the norm to live with friends. (4) Also, this is a bonus point but it’s known that most killers kill (or at least start) very close to where the live. It’s familiar territory and more comfortable for them — doesn’t get much closer than 30 ft…
I still lean in the camp of it being someone they knew but this alternative does line up with some of the other theories being discussed.