Papadopoulos was referred to as a 'proactive cooperator' in the legal docs. He was arrested way back in July and his name wasn't publicly revealed til today (late Oct). Therefore the suggestion is he was likely wearing a wire during the intervening time.
That would be quite something.
The question is... who else had Mueller flipped other than the obvious ones? I suspect he used Papadoupoulous to get some other low hanging fruit and had them doing the same thing.
Can you imagine the paranoia in those circles now?