Sure. Executor or not, stealing is a crime. How do you prove a crime? Someone took something that was not theirs and meant to keep it. Of course, this is tougher to prove when there is an executor involved, because executors are legally REQUIRED to take control of the assets of the estate to safeguard and preserve them. So unless you can prove that the executor did so with the intent to steal it and keep it for himself/herself, the court may not buy your argument. It sounds like you have a weird and complex situation. I would consult with an attorney to see how best to proceed.
*** LEGAL DISCLAIMER I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in your state. The law changes frequently and varies from state to state. If I refer to your state's laws, you should not rely on what I say; I just did a quick Internet search and found something that looked relevant that I hoped you would find helpful. You should verify and confirm any information provided with an attorney licensed in your state.
Yes anyone who steals can be convicted of a crime. However, to get a criminal conviction, you generally must get the police and prosecuting attorneys involved. The probate court likely would only deal with estate issues rather than criminal issues. Either way proof of wrong doing would be required. If your real goal is to get the executor out and the missing assets back, consult a local estates lawyer. Lawrence Friedman, Bridgewater, NJ. Certified as an Elder Law Attorney by the ABA approved National Elder Law Foundation, former Chair NJ State Bar Association Elder and Disabilities Law Section, Member Board of Consultors of NJSBA Real Property, Trusts & Estates Law Section, Vice Chair Special Needs Law Section of National Academy of Elder Law Attorneys, and Master of Laws (L.L.M.) in Taxation from N.Y.U. School of Law.