Ever read Neal Stephenson's Cryptonomicon? The WW2 part shows a team going through elaborate measures to create a plausible way that the allies can find out what the Germans are up to without revealing that they can read all of their messages. They would tell a submarine to surface at a particular location at a particular time and report what they see, for instance, and the sub crew would have no idea why, to produce a plausible explanation of why some German action was discovered.

Parallel construction often means they hide how they got the original information from the court and from the defense.