This isn't simply a "fill out a form" issue. This is a call the Head of Security and start a full investigation immediately issue. I would ask the client to draft a statement, in his/her own words, as to what they believe is missing and circumstances involving the item and/or box they believe to be important to the situation.
The client must be asked some very specific questions and the answers carefully recorded. When did you last enter the box? Do you recall who assisted you? Who has possession and/or access to your box keys? Do you recall when the item was placed in the box?
They should be asked to inventory all contents and acknowledge that all other contents are accounted for. The box should be closed and another opened, ensuring that all keys to the new box are provided to the client.
The entire situation must be carefully diarized. The customer should be informed that the bank is very concerned and takes its processes to safeguard box contents very seriously and that a full investigation will be conducted (including review of box entry records, vault entry films, etc.)
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