If a bank thinks money laundering has occurred, and the police don't request to seize the funds, then normal behaviour is to return the money to source, or even to the customer they suspect of money laundering.

Banks don't have any actual power to seize funds, only the police do that, and it occurs extremely rarely. (I've seen thousands of reports sent to police every month for years, and I've only seen police seize funds a handful of times)