Yeah, I also suggested to Dazza to try the way to report that to the authorities/police. Not, because there would be a chance get them in a lawsuit that would possibly involve 3 countrries in 3 continents (and would be more expensive than just to give up the biggest business in SL), but just to have the authorities knock at LL's door and ask for the RL data of the griefer.
LL CAN react quick and with suspending alts and even computers from access, they do that on other cases. In this case, a crime is done in SL (give me 100 kL$ to stop the griefing means: give me 400 US$ ... and that is blackmailing). As long as LL do not repond in a proper way, they might learn the hard way: having the authorities ask for the RL data.
If that would happen more often, they might think about allowing griefers so many ways to grief and residents so few ways to protect themselves and to be protected.
So reporting that griefer to the police would not aim at the griefer themselves, but at LL to think about if they let residents blackmail other residents (and hide behind: it's between residents, we can't do anything).
I think, Tateru made a good suggestion too, see, who you let on your sim ... however: if you want to get players to a game, it would not be good for the business to have them sign up to a group first. If you offer services like a big multiplayer game, gate should be open (though it's risky).