I've deposited thousands before and not been questioned about it, the banks only do what they are legally required to do and nothing extra, money laundering means more money for them.
Most banks take money laundering quite seriously due to the prison sentences for staff if they do nothing. While the bank may well like the extra cash most of the staff would prefer not to do five years to make them a bit of extra profit...
) as you could get into trouble for that. But nothing can happen to you if you dont touch it as its not your fault and youre not held responsible for going out your way to rectify someone elses problem. Banks couldnt give the slightest about your good will gesture of reporting it either. IMO anyway.



