I think at this point you need to bring in the principal (if you haven't already) and the superintendant. Make sure you have proof of criminal activity, then seek their recommendation about whether or not you should go to the police.
Our PTA has quadrupled in membership this past year. We are developing a great relationship with the Teachers and Administrators, in particular and have seen a lot of community support. Unfortunately, we have an unscrupulous Member/Fundraiser Chairperson. 1) posting unauthorized notice of scholarship. 2) Unaccounted for funds in the hundreds of dollars. 3) Purchasing equipment with PTA funds and keeping it. 4) Over budget in more than one venture; chairing a huge event and nearly bankrupting the organization. 5) Excusing volunteers from their posts and committment; just to name a few issues. There are actually two people involved....the buddy system. The second is a new board member.
We, the other board members, have a decent plan of action, but are asking your advice. (Much of it is actually criminal action)Thank you for you viewpoints.