Was it their watch post or were they guarding it so he could use it?
Take a look at the photo, behind the small kid, you can see an ac unit that is on the side of the building joining corridor that looks like it could be climbed on to gain roof access. It is on the opposite side of the building from the where the ladder in all the photos is. The story that crooks used the ac plausible from this picture(not 100% since you can’t see how close the ac unit is to the building connecting corridor.