I agree there were probably no cams in the auditorium, but if SP killed Missy in the SW corner of the building, there were 3 hall cams in that area (according to ArkansasMimi's and Nancy Grace's diagram of that corner by the awning). So, JMO, but I don't see SP cutting through the auditorium from a perimeter room without setting off one of those motion-activated cams. (Unless disabled.) And seems he'd have also set off northern hallway cams when he crossed from auditorium to kitchen, again (unless disabled).
I suspect the ONLY interior cams were in the halls. So the only chance to see the perp on cam is when he was in the hall AND when the cam turned on.
I also think (but don't have any way to prove it) that there would be a short lag time for the cams between "activate" and "record." If they are already recording, they get all the movement, but if not, and the action in the field of vision is brief, then it would capture nothing.
That is to say, I suspect you can't walk slowly down the halls, or any distance down them, without the cam recording you. But if you happened to run across the hall, from exterior room to auditorium, you might.
Also, the "SW corner of the interior" might have meant the SW corner of the auditorium, which would further limit any opportunity to see the perp after the murder. Just a quick run across the hall from auditorium to kitchen, and out that outside kitchen door.