An oft-oerlooked technique in "information management"...
...is the pacing and timing of information release, as well as it's content. A flood of data can overwhelm analysts, until it's too late to do anything about it, or until public curiosity or press interest dwindles.
Another possibility is "data dilution", where real nuggets of information which can no longer be hidden are embedded in torrents of routine message traffic. This also obscures clever removal of certain items from the record. Remember the "18 minute gap" in the tapes?