Is the action described below criminal?

While an executor or administrator is not authorized to act before being formally appointed by the Court, lawyers commonly advise them to lock the house beforehand to prevent theft from the estate.  In this instance, you are the executor.  If you have been appointed from the Court, ask your probate lawyer to file a Motion for an Order to Show Cause or a Motion for a Turnover Order.  An Order to Show Cause orders the person to come into court to explain what cause they had to do what they did.  A Turnover Order orders someone to turn something over (in this case the locking mechanism).  While this fellow may eventually inherit, it is your duty to assemble the property, compile an inventory for the Court, pay the debts and distribute the rest.  This definitely includes accessing the property in the house and may include selling it to pay the debts. Your own property in the house is another question.  But once the Court's Order is in place, you should have access to it. All this legal work is a cost of the estate.  If the estate is small, having to do it may mean that you will have to sell the house.  The person who changed the locks might be apprised of this.