The SAR Activity Review – Trends, Tips & Issues (June 2001) addresses the filing of SARs on continuing activity after law enforcement as follows:
Questions have been raised regarding the necessity for the continued filing of SARs on continuing activity after law enforcement has contacted a financial institution with regard to a SAR filing. In some instances, after the filing of one or more SARs, law enforcement has contacted a financial institution requesting more specific information with regard to the suspect activity or requesting identified supporting documentation. In other instances, a law enforcement agency has contacted a financial institution to report that it does not intend to investigate the matter reported on the SAR.
If conduct continues for which a SAR has been filed, the guidance set forth in the October 2000 SAR Activity Review (Section 5 - Repeated SAR Filings on the Same Activity) should be followed even if a law enforcement agency has declined to investigate or there is knowledge that an investigation has begun. The filing of SARs on continuing suspicious activity provides useful information to law enforcement and supervisory authorities. Moreover, the information contained in a SAR that one law enforcement agency has declined to investigate may be of interest to other law enforcement agencies, as well as supervisory agencies.
FinCEN’s SAR Activity Review information may be found here: https://www.fincen.gov/sar-activity-review-trends-tips-issues