That bring us back to trespassing - he was let in by the person in charge at the time. Mott claims he just walked into the building -- which is trespassing.
The school claims that Mott banged on the door and the janitor let him in because of the uniform -- which is an improper use of the uniform by Mott.
The truth may be in the middle -- which means that both sides are lying. Which still says that Mott was trespassing.
where are the no tresspassing signs. (don't give the he was a cop excuse) If you are going to hold him to the same rules then he gets the same rules. The custodian could EASILY have not let him in. But he did, once in he was an invitee and the presence was valid. (see also bowers vs. hardwick where a deputy was let into an apartment to serve a subpeana and was unfortunate to walk in on an illegal act.)