Slandering his name?
Hah thats funny - And what he is doing to you is nothing of the sort, of course
As far as I am aware you have done everything to protect the identity of this person from the public as to prevent them from being treated in the manner you were - Any legal action this user will be taking is defending himself in court if you persue a legal course - I recommend doing so, and I will even be your lawyer if you want - I have no legal standing, but I would so love to verbally rip apart the little snot-nosed punk in a courtroom
Satan