[justsomeguy]

Originally Posted by AC-Phoenix

Which is wy she wasn't the one opning the door. Only two person's qualify to be the murder in this case - namely The guy who opened the door and Kounuso.
The latter got my attention when they stated in episode nine that the rope was relevant to the case in some way, before it was Katsuta. Since we never had a chance to examine whether the door was really closed it is also possible that he only pretended that it was locked in the first place.

Lets now assume the door was really closed, which does indeed only leave Kounosu, BUT just if you know about the rope.
Either way she would have trouble climbing up the chute without the rope, no matter if its a food elevator or a laundry chute.
There are several ways to enter the room but only one to leave.
(Except if you accept that thing next to the safe as a trapdoor but that would defeat the rope's purpose)

It cannot be the guy in yellow in any case. He was on the same side and level of the building as the girl in blue, and his movements would have been seen by her, and possibly by the guy upstairs. He cannot go to backstage right unless there's another passage unaccounted for. The possibility of him being the perp is even harder to argue than Kounosu's.

If by "that thing next to the safe" you mean the fallen door to the opening up on the wall, the wall opening looks otherwise sealed.