Fraud by a customer to the Banker - Banking - Finance

Sir I m a cashier working in a bank. A customer came for cash withdrawal instead of debiting the account, I, by mistake, credited the account. Now, customer has taken physical cash from the branch. Seeing more balance in the account, the customer made withdrawals using UPI and ATM. I informed the customer immediately when I found the cash difference on the same day. Now, it has been 3 months and the customer has not deposited a single penny. FIR was not lodged as the customer kept on asking some more days and then weeks and now we have realised that it s quite late to lodge an FIR. The customer is maintaining accounts in 2 different banks and one account in another bank as second holder. What action can I take now to recover the money? The amount involved is more than 50,000.