Killing a troll is never easy, but rather than threats I think the answer is silence.
If ALL members restrain themselves and simply never, in any way, respond to the troll he'll usually wither up and die.
Trolls feed on attention and feedback, and even a negative response, or even especially a negative response, is fuel for more acting out.
Not being part of the site's admin I can't suggest what else to do - but on my site the mods delete all troll posts and sock puppets immediately without comment - it kinda takes the wind out of their sails!
Ignore the jerks and enjoy the rest!