Please back extraordinary claims with evidence. From where I live, there is nothing in the law that says the bank must leave you hanging dry in case they detect fraud. If it’s different elsewhere, I sure would like to see concrete proof of it.

If you make a large cash transaction, the teller is not supposed to tell you they are filing a Currency Transaction Report (CTR). If you ask about the CTR threshold and then change your transaction size, the teller is then obligated to file a Suspicious Activity Report (SAR). Both CTRs and SARs are reported to Treasury.

It's not about fraud, it's about money laundering. They often look like the same thing.