So then is this very crude drawing I made the most likely path of the killer? Red is where he would've entered and gone and blue is the route back out when finished. The 'X' markings are where murders physically occurred.
I put a question mark next to KG on the third floor because several reports had mentioned that she was in the process of moving out and that weekend was one of her final trips back before taking a job in another state I believe. Someone please correct me if I'm wrong. The question mark is it hasn't been confirmed yet that her bedding, frame, etc. was still in her room so there has been speculation that she was sleeping in MM's room.
The stairway you sketched out is actually the one that goes downstairs from the LR to the 1st floor.
The plans you have don't show the stairwell from the 2nd floor to the 3rd floor. I believe they are in the boxy area labeled as "Foyer" on those plans.