In Neal Stephenson's brilliant Cryptonomicon, a protagonist works for a shadowy Allied unit called "Detachment 2702." Detachment 2702 creates elaborate fake evidence to offer explanations of how the Allies learned of German movements, thus concealing that the Allies had cracked the Enigma code. Though fictional, the Detachment is based on actual World War II tactics. The Allies did things like send spotter planes to places they knew German ships would be to fortuitously "spot" them, and reportedly sent a fake radio message of congratulations to a non-existent spy to suggest a source for other intelligence.
You expect the government to use secret surveillance and disinformation campaigns against a wartime enemy. You probably don't expect the government to use secret surveillance and disinformation campaigns in court against its own citizens.