Stage right contains both the stage manager’s position and the prop box. The stage manager’s table is visible in this bird's eye view. The light is on and you can see a copy of the script open on the table. Rex was last scene passing through the door in the room scene into this area and only to be discovered dead in the prop box after the scene was over. The obvious question is when and how did that happen. There was about a ten minute period after Rex finished his talk before Nick took up his position at the stage manager’s table to start act three. So Rex could have been alone here, or not alone. Susan the light girl had an interesting suggestion that something illicit was going on and Rex interfered it and got killed. All that would have had to happen in just ten minutes. Maybe. Nick the stage manager can see the prop box from his position and insists that nothing at all happened there during act three. But light girl Susan says that just after the curtain went up for act three she thought she heard voices on the intercom and then it want dead for quite a while. And when it came back on it sounded like Nick was out of breath. But the bit about Nick being out of breath might have been her imagination.