We have business loan customer in reviewing their financial statements, we discovered and they admitted that they have not been filing tax returns. Should we file a SAR in this instance?:

Is failing to file a tax return and pay the taxes a federal crime? Yes
Do you have reason to believe the customers have committed that crime? Since they admitted as much, I'd say again, Yes
Do you have any idea whether the amounts involved exceed the reporting threshold of $5,000? Probably yes.,

Sure sounds like a SAR filing to me. I pay my taxes and file my returns, and I don't take kindly to those who don't pay what they owe.

The difficulty with filing these types of SARs is the date range and dollar amount.

I don't like tax cheats either.

I've always thought Tax Evasion was an underlying crime, such that FinCEN removed Tax Evasion as a box on the SAR, if I'm recalling correctly. Would you file for loan fraud and use the loan amount?

I don't recall that Tax Evasion was ever a box on the SAR form.

We check "other" and type in possible tax evasion.

I wouldn't file for Loan Fraud in this scenario, since there is no indication that the applicant made any misrepresentation.

Where I would struggle to even consider filing at all in this instance, is identifying what part of the suspicious activity took place at or through the bank.

Agree. Without any transactions funneling through the bank, there is no means to complete the SAR form.