The below is my proposed explanation that accounts for everything we know, with a map. It has her entering SW corner, cam losing sight of her as she goes farther down the hallway, her body being found in the "southwest corner of the interior of the building" in various possible meanings of those words, and it allows for an unseen-by-cam path to the kitchen door exit.
1 MB enters the SW doors under the awning area, as noted by blue arrow.
2 As she does, she is picked on cam, first by the cam noted as c1 which has a peripheral view all the way into the vestibule itself.
3 As she steps further northward up/down the main hallway, she is picked up by cam c2 which is looking over her shoulder.
4 Perp is lurking ahead, in one of the locations noted (P1, P2, or P3), having been seen by the cams earlier but not seen by MB as she enters and takes that stroll.
5 P1 - a guess at a possible location of the perp when MB entered the halls - would be in a recessed area into the doors into the auditorium (same with P3 area).
6 As she moves further up/down the hallway, per the arrow, the cam c2 loses sight of her movement and stops recording, and sometime shortly after that perp attacks.
7 Perhaps as he attacks, he pulls her out of the hallway. Perhaps she is first subdued then dragged to a spot, perhaps not.
8 Ultimately her body ends up in one of the places marked by an X, or maybe at P1 or P2 location, all generally in SW corner of the building's interior.
9 From any of those spots, an unseen-by-cam exit could have been possible out the kitchen door on N side of building, as LE believes.
10 The theorized places noted, where the body might have been found, have an important element - they allow an exit unseen by cam, yet out the kitchen door, as LE says happened.
11
A red line shows an unseen-by-cam path from one proposed body location, to the kitchen door.
A purple line shows an unseen-by-cam path from another proposed body location, to the kitchen door.
12 Camera c3, in far right end of northside hall (NE corner of building), shows where the closest known cam is in that northside hallway. I'm theorizing it didn't detect motion that far away, and thus didn't record, when perp exited.