Once again, Yes Minister explains the US Government

The DoJ can't investigate the NSA's surveillance program because it can't get the right clearances.

Brian Roehrkasse:

Brian Roehrkasse, a Justice Department spokesman, said that the N.S.A. program was "highly classified and exceptionally sensitive" and that "only those involved in national security with a specific need to know are provided details about this classified program." He said the legality of the eavesdropping program had been reviewed by other Justice Department offices and by the N.S.A. inspector general.

Sir. Humphrey Appleby:

The Official Secrets Act is not to protect secrets, it is to protect officials.