Update #25 The CCTV Map
Adam has posted a photo.
This map shows the locations of CCTV cameras around the school.
Tapes 6, 8, 9 and 10 have been taken by the killer in order to cover his (or her?) tracks. By marking these locations on the map we can see the route the killer must have taken after the murder, which I've marked in red.
I think Matt's body is in the gym.