From the start I didn't think the two surviving roommates were directly involved and after creating the floorplan I can see why they possibly didn't hear anything. If the killer took the path in the attached image (the red line) they didn't even walk on the floor above either of their rooms. Not to mention, Bedroom #1 is right next to where the utility closet with the furnace is located so it's conceivable that the furnace was making noise assuming it was cold at the time. Also Bedroom #2 is very far from the assumed bedrooms of the victims. This also assumes that E+X were in Bedroom#3, M in Bedroom #5 and K in Bedroom #6 with Bedroom #4 being unoccupied. I also don't think the front door and lowest floor were involved at all. To me the killer was in less of the house then I initially imagined and probably for a shorter period of time as well. Whether this means he knew the layout of the house, I have no idea. All IMO of coursebl
My opinion only but I think Kaylee was killed first, and then Maddie, (which would be more risky since her bedroom is directly above another bedroom, potentially X+E's room). When stabbed, the murderer would have to put some weight on the knife and possible be on the bed restraining MM with his other hand? EC may have heard the thump and went to check on this as murderer is coming down the stairs and E was attacked possibly by the doorway of the bedroom, which looks to be visible from sliding doors (important later). Murderer then attacks X because obviously she's awake and would be a witness. At this point, murderer is caught off guard and leaves as soon as he can since the confrontation with E and X make a lot more noise than he planned. He doesn't risk going down to the main/lower level, because if he needs to make a quick getaway, the only one way out is back up the stairs to the front door to the street. Or if he thinks roomates may have called cops during all the commotion, cops would likely enter in the front door.
He leaves the house through the sliding doors back to the wooded area, and walks a bit to his car and drives off. I believe he had tactical gear or removable PPE that he was able to fold up, put in a trash bag, into his backpack.
The person that visits the house the next day tries to call one or some of the victims and gets no response which is odd. He goes to the house and goes to the back slider door, looks in, and sees Ethan lying across the room by the bedroom doorway. He (or she) then calls 911.
I believe the murderer has watched his intended victim(s) from afar, likely in those back woods behind/side of the house. He likely owns binoculars, tactical gear, night vision goggles, etc. He may even have gotten the trust of the dog during the times the dog was let out at night with high value treats in that bushy area. It's possible he's been in the house before, to do a trial run.
He feels very content with himself and feels giddy when he hears they have no leads or the wrong people are getting blamed.
This is how I'm envisioning it happening.
