You may need to have the estate pay for legal defense to not only have a reassignment of the executor but to sue all who you believe are involved in the theft and to ensure those individuals (if more than one) pay the estate back/give back the coins and pay for the attorney costs.  At the end of the day, the executor has certain responsibilities and to ensure that the estate assets are not wasted and in most circumstances that the assets are kept safe.  If you know who did it, you should immediately contact both counsel and the police and get the process started to get back what you need.