Though I find it funny and quite a "freaky" coincident that one guy, from the same island of 1.2 million people in population who uses the same service as you, contacts you on a board for [Something], then contacts another [for blackmail], signs a new user up under you, contacts the "blackmailee" to use that account and just lets it pass for no benefit for him (??) ....
I don't really care how IPs work on ".MU"... What I care about is that everything points towards you and that I have no moral issues regarding what I've done (I'll fall asleep tonight and sleep very well).
The guy is on this board. He will be following this thread and if he chooses to get in touch with you, then that's his decision.