You wont, because of a little thing called Parallel Construction. NSA finds something out illegally, unethically, they pass it to another agency so proceeds

You wont, because of a little thing called Parallel Construction. NSA finds something out illegally, unethically, they pass it to another agency so proceeds to figure out a way to "discover" what the NSA did in a way that is legal, or at least plausible to the courts, thus never having to admit the investigation started with the NSA