The SAR Activity Review – Trends, Tips & Issues (June 2001) addresses the disclosure of SAR documentation:
Under the SAR regulations, institutions filing SARs should identify within the SAR, and are directed to maintain all "supporting documentation" related to the activity being reported. Disclosure of supporting documentation related to the activity that is being reported on a SAR does not require a subpoena, court order, or other judicial or administrative process. Under the SAR regulations, financial institutions are required to disclose supporting documentation to appropriate law enforcement agencies, or FinCEN, upon request.
FinCEN’s SAR Activity Review information may be found here: https://www.fincen.gov/sar-activity-review-trends-tips-issues