"4. Exactly when did #2 leave the observation post? Go downstairs? Leave the building? Try to come back in?"
It seems to me that use of the door (or roof access window) seen in the picture below, would allow one to get a full view all the first storey roofing. Its use would by natural for anyone with familiarity of that indoor 2nd floor area. A person could get back into the A/C in no time flat.
