You have no responsibility to someone trying to commit fraud. If I tell you to promise to keep a secret, and then reveal to you that my secret is that I am a lifetime conman or a serial killer, you do not have a responsibility to keep my secret.

On the contrary, you have a responsibility to let people know who is attempting this fraud, so that people may protect themselves from this scum. He's likely conning unwitting people in the Bitcoin Marketplace right now.

So, who is it?