Legal Question in Business Law in California

You need to operate within the formal management and control laws, rules, etc. governing your type of nonprofit organization. Generally, California nonprofit corporations have a board of directors that are vested by law with power (and duty) to manage the organization's affairs, including hiring and firning employees. There will also be Articles of Incorporation and probably bylaws. Most likely the Board will need to meet and vote, then the manager should be given written notice to return all money, keys, documents and records, etc., and the possibility of legal action perhaps should be mentioned. If there is a significant risk of problems, such as the disappearance of money or records, you might want to consider retaining an attorney, a CPA, or both to lend some muscle to the return-everything demand. Be sure to have the books, records, accounts, etc. examined afterwards. Perhaps have the post office re-key the mailbox and change bank signature cards.