That would work out very badly. Consider this cold war example: Somebody high-up in the CIA is secretly working for the USSR. They are passing everything to th

That would work out very badly. Consider this cold war example: Somebody high-up in the CIA is secretly working for the USSR. They are passing everything to the USSR. Over in the USSR there is a similar situation, with somebody passing KGB things to the CIA. The guy secretly working for us is able to reveal the person secretly working for the USSR. Now we grab the person. If we reveal the evidence to him and everybody in unclassified court proceedings, it will get back to the USSR. Our agent in Moscow will be caught. Even if we black out his name, he will be caught. It's a scary enough risk just acting on the info he supplied. Your way of doing things gives us 3 terrible choices: a. Evacuate our super-valuable guy from Moscow. b. Get our guy in Moscow killed. c. Let the spy go unpunished, thus encouraging others.