1) Obtain information about a crime via method you don't want made public (classic example is ongoing undercover work or ongoing wiretap)
2) Have someone tell a CI, then have CI report it back
3) use report to follow up and obtain sufficient justification for warrant
4) actual source of the tip is never disclosed in court.
Not saying that's what happened here because the NSA doesn't give two shits about some guy that filled out a few fraudulent tax returns, just pointing out that that shit never show up in court. That's also why very few espionage cases are brought to trial.
1) Obtain information about a crime via method you don't want made public (classic example is ongoing undercover work or ongoing wiretap)
2) Have someone tell a CI, then have CI report it back
3) use report to follow up and obtain sufficient justification for warrant
4) actual source of the tip is never disclosed in court.
Not saying that's what happened here because the NSA doesn't give two shits about some guy that filled out a few fraudulent tax returns, just pointing out that that shit never show up in court. That's also why very few espionage cases are brought to trial.