"He doesn't have to go up the steps" is said multiple times and it makes me zone in on that comment even more.
Could he possibly be implying that the killer(s) did indeed enter on the 2nd floor, and that they didn't have to go to the 3rd floor to cause harm, so why would their "points of damage" different on the 3rd floor? ( M & K ) - unless one was "targeted" more than the other?
Edit to add: Or to conflict some of what I said "he doesn't have to go up the steps" could also imply that neither M or K was the target - so as usual with this case my head is just going in circles.