In the State of Minnesota, upon the death of a customer the bank can only grant access to a court-appointed person except in certain limited circumstances (very limited).
When the customer opens the box, they can appoint a deputy but that relationship is severed upon the customers death.
The Minnesota Bankers Association has a Safe Deposit Box manual available. It is very helpful.
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Sometimes you have to burn a few bridges to keep the crazies from following you.