Mr Church was the one that uncovered the printout, and he was the only one there, meaning no one would have known if he had staged the whole thing, and made that printout himself. The super computer also simply said it would take approximately 90 years, and had said nothing about the system overloading or anything of the sort. This makes it likely that Mr Church staged the explosion to stop Mr Gibault from discovering the thief, even if it took decades.

Furthermore, that printout had WAY too much information for something that had been projected to take multiple years; decades, even.

Seeing that Mr Church had been the one to forge the printout(in my theory at least) it seems odd he would clear the names of a select few. Furthermore, the computer was never asked for the names of the innocent, just the thief, making this even more suspicious

-

UNLESS

-
they were in his little group of elixir thieves(?).

Mr Gibault also happened to be in a meeting with Mrs. Kim, Mr. Coogan, and Mr. Knox(who had all been cleared by the printout - suspicious much? - ) leading me to believe that they had been distracting Mr. Gibault while Mr. Church made the forged printout.

Mr Coogan with his "legendary sense of smell" also could have easily led Mr. Gibault to the perpetrator after ending up in the office. It shouldn't be hard since not many people crawl out from under tables, but he doesn't; once again, because he is one of the criminals. This also explains the suspicious behavior from not one, but most of the teachers.

This part of my theory is from episode three: if most of the 8th grade teachers DO happen to be the group of perpetrators, it explains why Mr. Knox went so easy on Mr. Coogan during the interrogation. For us, of course, its meant as comic relief, but seriously; that was in no way a proper interrogation.