For me, much would depend on the seriousness of what you claim. Bear in mind that because you "have a case" does not mean you will win. If you do win, it does not mean he will be dethroned and you could make life extremely unpleasant for yourself. And yet he still survives... Bear in mind that your position at the school could be made untenable if you go down this road. Not fair, but realistic. I am not going to say "Don't do this" but I would say be very careful in whatever you decide.