The Silvermaster File[1] of the United States' Federal Bureau of Investigation is a 162-volume compendium totalling 26,000 pages of documents relating to the FBI's investigation of GRU and NKVD moles inside the U.S. federal government both before and during the Cold War.
[19]) Among dozens of others named by Bentley in this file in connection with this network is Duncan Lee[20] (Venona cover name "Koch"[21]), confidential assistant to William Donovan, founder and director of the Office of Strategic Services (OSS), wartime predecessor of the CIA.
Original plans for Bentley to serve as a double agent and gather sufficient evidence to prosecute the Soviet agents identified in the Silvermaster files were ruined when her identity was inadvertently leaked and the USSR quickly shut down its operations.
The Silvermaster file in combination with other secret proofs such as the Venona intercepts gave US intelligence the identity of many Soviet agents without the practical means to secure convictions.
Bentley's double agent career would have enabled the US to expose the spies without compromising Venona and losing that as an ongoing intelligence source.