Folks:
There are several issues in play simultaneously here:
1. Apparently a verbal notification only of a stolen item from the customer;
2. The law enforcement agency's inability to act because no report is on file; and
3. Your inability to act legally because no affidavit of forgery or theft report is on file.
Even if you know your customer well, please don't take the customer's word via a telephone conversation that an item has been stolen, altered, counterfeited or forged. Except in extreme circumstances, always require your customer to file written documentation that allows you to file a report of an attempted crime with your local law enforcement agency.
The agency needs this written report in order to be able to act. You need this written documentation in order to be able to represent the bank's interest and to therefore cause the law enforcement agency to act.
An attempt to commit a crime is still a crime. When an offender presents a stolen item for negotiation, the offender is making the institution a co-victim. Every victim has the right to file its own report with the law enforcement agency.