I get where you are coming from, but I disagree. Unfounded accusations should never be a viable weapon, and if you act against an individual without even a shred of credible evidence or corroborating witnesses, a weapon is exactly what you have created. You will have done real, lasting damage to a human being without any due diligence, whatsoever. If it seems likely a crime has actually been committed, only then can you justify irrevocably tarnishing their reputation and relationships with students, parents, and the community at large. The "correct" course is a discrete, but thorough, investigation to determine if something more intrusive is warranted. In cases like this, it is guaranteed that someone will be lying. Best to get a clue as to who before you start punishing people.