This time, during recess, I won't be walking downstairs to the auditorium. Instead, I'll head to Mrs. Brooks' office. We've agreed to take a look at what we've gathered together today and see if it contains anything useful to take to the police.
When I knock, Mrs. Brooks is already at her computer, with an empty chair next to her. I sit down, and we briefly review what I've seen over the past few days. Then Mrs. Brooks tells me about her findings; she's done a good job because she's reviewed the old schedules and created a timeline of who was where and when. It shows that multiple people had access at the time of the theft.
We also figure out that the boardroom was cleared out between 2:45 and 3:15 PM, which was during the last hour. Then I notice something's not right; I was at the lockers at 2:50 PM when I heard someone; so the break-in must have started much earlier to find and take everything.
At that point, we reached a joint conclusion: the perpetrator had the key and knew exactly where the documents were to get out in time; it was an inside job.