I'd like to repeat, because this is important: a red flag DOES NOT trigger filing of a SAR as was told to the customer. It only triggers an internal (i.e. only by financial institution) review of the account, especially with the amount involved in this story. Depending on the findings, however, a red flag may trigger continued monitoring of the account, based on the financial institution's policies.
One thing is certain, paying off loans (any kind) is one of the typologies already identified for laundering money and financing terrorism. This, BTW PRE-DATES Patriot Act - as does much of the information found in the BSA document mentioned before. What has changed after PATRIOT Act is the increased enforcement of the laws.
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Always question the motives behind a bank telling anyone that it was required for them to file a SAR. First of all, it consitutes "tipping" (letting the customer know that they have filed a SAR on them/their transaction - a big NO-NO. Second, many financial institutions have been lobbying congress for less regulatins because, guess what, implementing all this costs them money.