@Goldfish, I trust you with any full combat plan, but I know what I'm talking about here. There is absolutely no reason to reveal that we know he's being watched. In either scenario, we only do one of the following.
1) Reveal he's been skunked. He's complicit, we have to not only dispose of him but reveal that we know we were being watched. Now the enemy is on guard.
2) Reveal he's been skunked. He's
not complicit, but we can't find out who was watching on the other side. We might be able to find where it was manufactured, but we can't move on it right now. Or worse case, we have something that requires a full action to research for Intel, when we plan on moving against this same ring of informants and saboteurs next turn, making it a pointless gesture.
Contriving to keep him here is for the best, at least for the short term. We have to investigate him some point in the next turn.