Professor Edward Kane:

It is more a matter of the incentive for the manager to hide losses. It is not as if auditors can see anything. When a bank makes thousands of loans, the auditor can only sample them. In sampling them, it is in the interest of the bank to make it difficult for the auditor to find the loans with the biggest losses. They can take the files out of the bank for a while, if they are clever enough. That would, of course, be fraud but if it cannot be proved it might be worth the risk to keep their jobs going for another year.