When it comes right down to it for banking purposes, we always had a policy that if income wasn't on a tax return, it didn't happen. It was like a tree falling in the woods when no one was around. If someone wanted to cheat on their taxes, the penalty was that they couldn't use that as income at our bank to justify a loan.
As far as the SAR, if you can't verify the income, how can you suspect tax evasion? Is re depositing unsubstantiated amount of cash into his accounts. If so, I would approach it from that angle.
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