When what you are being blackmailed over IS a crime, the circumstances are a little different. But just to be on the safe side, I would probably recommend shooting all involved. The most guilty has to be in there someplace.
What?
How about being on the safe side and getting ALL the FACTS involved before you determine everyone should be shot?
So punish him for the underlying crime. But he’s also a victim — a victim of blackmail, and that is not a crime. It’s the blackmailer who’s the criminal in this case — but instead they choose to go after the person being blackmailed (probably for political reasons.)