The Feds Arrest someone and keep it secret..., Usually the smallest fish they can find.
They ask the guy to proffer what he has as far as enidence against the bigger fish and what evidence he has.
If he has something good and can back it up with evidence (including a wire) they let him plede guilty to what he was originally arrested for, otherwise they load the guy up with additional charges and bury him.
Papadopoulos was arrested, wore a wire and was allowed to plead guilty several weeks ago... if I had spoken with him during that time id desperately be trying to remember what I said. Someone is getting indicted based on that information Papadopoulos provided.