There are many accounts of the NKVD insisting that anyone released (usually after 1938) should sign a guarantee not to reveal what had happened to him in jail. A Soviet newspaper recently quoted one such:
I, Sternin, N.V., pledge never and nowhere to speak of what became known to me between 11 June 1938 and 11 July 1939 about the work of the organs of the NKVD. It is known to me that on any breach of this I will be accountable under the strictest revolutionary laws, for divulging state secrets.
-- Robert Conquest, The Great Terror: A Reassessment.
The Bush administration has told a federal judge that terrorism suspects held in secret CIA prisons should not be allowed to reveal details of the "alternative interrogation methods" that their captors used to get them to talk.
The government says in new court filings that those interrogation methods are now among the nation's most sensitive national security secrets and that their release -- even to the detainees' own attorneys -- "could reasonably be expected to cause extremely grave damage." Terrorists could use the information to train in counter-interrogation techniques and foil government efforts to elicit information about their methods and plots, according to government documents submitted to U.S. District Judge Reggie B. Walton on Oct. 26.
-- Carol D. Leonnig & Eric Rich, "U.S. Seeks Silence on CIA Prisons: Court Is Asked to Bar Detainees from Talking About Interrogations," Washington Post, Nov. 4, 2006.