I'm chiming in here kinda late, since I just ran across this discussion.
I'm not really qualified to advise anyone regarding whether or not to contact the authorities in a case of this nature, especially since there are probably more pertinent details than can be fit into a post on this board.
That being said, the smartest thing that you could do right away is to insist on an audit of the books being done immediately. If there is a thief in your midst, this may not be the first time you've been robbed. If an audit finds that more funds are missing than you were aware of, then you have a much stronger case for going to the authorities.
Regardless of whether or not you go the legal route here, there are a few things that you absolutely must do.
1) Get Parent Group Insurance ASAP! This protects ALL of you, not only from issues of theft/carelessness, but from other issues as well. This is available both through PTO Today and PTA (if you're affiliated with them). It isn't that expensive, especially when considering the alternatives.
2) Review your accounting and cash handling procedures and incorporate them into your Bylaws and/or Standing Rules. You should also include a copy of a detailed document in your Treasurer's Duties.
3) Consider purchasing a safe to be installed at the school, or ask if you can use the one at the school if one exists. Either allow no funds at all to be taken home with anyone, or limit the amount that can be taken home with someone to a small amount. If an event ends late at night and the deposit can't be made immediately, two of you can witness that the money was counted and then put into the safe. The funds can then be pulled from the safe and taken to the bank the next business day by two people (Treasurer + 1).
4) If the safe idea isn't an option, and if your bank doesn't have a night deposit drop to enable immediate deposits, consider getting locking bank bags and making certain that the key and the bag are never both in the possession of the same person. In this case, this simple and inexpensive step could have saved you a lot of trouble, since the person with the key would have been quickly aware that the deposit still hadn't been made, and two people would have been present the entire time that the money was being handled.
5) Establish online bank account access if possible, and require that the username and password be accessible to both your treasurer and one other person at all times. This will let someone other than your treasurer check the bank accounts and be aware rather quickly if deposits haven't been made or if unauthorized checks or withdrawals are taking place.
6) Make certain that all members of your organization who handle money know that they shouldn't hand over money to anyone without a receipt for the amount that they are handing over. This protects them personally as well as your organization as a whole.
7) If you haven't already, make certain that all checks are required to have two signatures on them. This may very well be the simplest step of all that can be taken to ensure your group's financial security.
The argument that I most frequently here regarding these types of safeguards are that they are too inconvenient for some or all parties involved. But I can guarantee that they are a lot less inconvenient than dealing with the kind of problems that can result in their absence.
And for anyone who isn't currently in a crisis situation, but who has noticed some lax procedures in your group, you don't have to express any misgivings regarding your current board members to bring this up for discussion. Simply bring up one or two recent cases of embezzlement from the news as reasons for tightening up your group's rules and procedures now, before there is an issue. Point out that as much as you'd like to believe that the people elected to handle the finances of your group will always be trustworthy and honest that you are sure that these organizations in the news thought the same thing.
Regardless of whether this particular case does or doesn't go the criminal route, we should all take this as a good reason to go over our own group's cash handling procedures with an eye toward areas that could be improved. As officers we are being entrusted not only with the current activities of our group, but with its continued security.
~Lisa