That's what I was thinking too, but a senior officer said, why file a SAR when he's not doing anything illegal by staying under the reporting threshold and we don't have reason to believe the funds are being used illegally.
Showing the FinCEN pamphlet to that senior officer might help him/her understand that intentionally staying under the threshold
is the "anything illegal".
"Can I break up my currency transactions into multiple, smaller amounts to avoid being reported to the government?
No. This is called “structuring.” Federal law makes it a crime to break up transactions into smaller amounts for the purpose of evading the CTR reporting requirement and this may lead to a required disclosure from the financial institution to the government. Structuring transactions to prevent a CTR from being reported can result in imprisonment for not more than five years and/or a fine of up to $250,000. If structuring involves more than $100,000 in a twelve month period or is performed while violating another law of the United States, the penalty is doubled."