According to the BSA/AML Manual1, once a financial institution files a SAR, it should maintain a copy of the SAR and the original or business record equivalent of any supporting documentation for a period of five years from the date of filing the SAR. The supporting documentation should be identified and maintained by the financial institution as such, and be deemed to have been filed with the SAR. The financial institution should make all supporting documentation available to FinCEN or any federal, state, or local law enforcement agency, or any federal regulatory authority that examines the financial institution for compliance with the BSA, upon request. Therefore, the best action to take regarding a particular account once suspicious activity is reported by the institution is to secure all supporting documentation, as it may be needed for further investigation or examination.
References:
BSA/AML Manual1
Suspicious Activity Reporting - Overview2
Suspicious Activity Report (SAR) Basics3