It needs investigation. He would be indeed only idiot watching porn and masturbating just after the lesson. Lynching him is not wise idea if he wasn't raping any child and if it isn't yet proved he did it knowing children are watching - judging him it's the job for judge and juries.

But his behaviour was suspicious enough to think he might be paedophile. And firing him with forbidding working with children would be wise idea anyway. The rest needs investigation,but firing him would be good beginning.