Financial institutions must maintain records under which law to aid government investigations?

The Bank Secrecy Act (BSA) is the correct choice because it specifically mandates that financial institutions maintain records and file reports that can help detect and prevent money laundering and other financial crimes. This law requires banks and other financial entities to keep detailed records of certain transactions and to report suspicious activities to the Financial Crimes Enforcement Network (FinCEN). The BSA plays a crucial role in the U.S. government's efforts to combat financial crime by ensuring that institutions provide necessary information to assist in ongoing investigations.

The other laws mentioned do not specifically focus on maintaining records for government investigations in the same way the BSA does. The Electronic Signatures in Global and National Commerce Act primarily deals with the legality of electronic signatures and records. The Gramm-Leach-Bliley Act is focused on the privacy and protection of consumer financial information. Regulation Z, also known as the Truth in Lending Act, primarily deals with disclosure requirements regarding credit terms and is not aimed at supporting government investigations in the same capacity as the BSA.