Although this guy sounds like an unscrupulous scum-bucket who deserves nothing better than to have his head handed to him in small claims court, I think your organization would be far better off spending your time and energies shutting down any access he has to your mail/accounts, etc. and moving on.
Chasing after him for the tricks he pulled seems reasonable, but it will drag on forever and will drain everyone involved. Plus, the outcome isn't, no matter how much it seems it should be, guaranteed to be in your favor. Judges can do strange things when having to pass judgement against a well-connected citizen. So, just say "next!" and focus on re-building instead.

Our membership re organized at the end of last year. We are a High school parent org that renamed ourselves a "parent council", since we had absolutely no teacher participation. For the past year the previous PTO president has refused to hand over any information because we dropped the PTO name. It has just come to our attention, thru a thank you note from the Board of Ed, that he has donated the money in the PTO acct to the school. He strung us along all year with reasons why we could not have control of the acct, that he had left letters authorizing us to take over the acct, and other really confusing statements. He claims we authorized donating the money based on a comment I made in frustration stating that if he refused to hand over control of the acct, he should just donate it, rather that let it be absorbed into the school district budget(his claim). We know full well, as does he, that any distribution of funds must come to a vote by the general membership. Our understanding was that when we voted in the new name, all accts, information etc. was transferred. Our treasurer has sent a letter to the principal explaining the situation and requesting the money be given back. We have also had to close our mailbox at the school as we find opened mail. There is some discussion about filing charges and taking him to small claims court. The acct totaled $475. Frankly that scares me to death as this guy is the vice chair of one of our local political parties and has his fingers in everything. He also does not presently have a child in the school system, they have all graduated. This has become a really big mess, any advice would be helpful.