Here's the pic you mentioned.Please correct me if I am wrong. If that area across from SP is, in fact, the hallway leading to the main doors, this picture is the NW corner.... looking south (west would be to the right).
If a person is heading east (walking from the main doors toward the western hallway) and turns left, that person would then be north. What I am wondering is, "Is the camera covering the western/main hallway actually mounted in the NW corner (and not the SW corner as previously thought)?" That would explain MB getting "out of range" as she walked toward the SW doors. It might also provide a much larger blind spot for MB's attack than we previously thought.
ETA - Look at Camera Two's coverage. If you look at where the green stops, quite a bit of hallway at the far end is not picked up because it is "out of range". Are we 100% positive about camera placement? I think that the camera we are seeing in the bottom left of NIN's picture is mounted in the NW corner looking south.
In the pic above, perp would be standing where marked below.
The opening to the right in the pic/diagram above (more or less across the hall from the perp) is a recessed entry into the auditorium, and is not the main entrance (way too small). Also, in the video that pic was clipped from, the perp keeps walking south and a few frames later at the bottom right you can see the corner where the southside hall begins.
Hope that helps.