Originally Posted by AntonMG

Option A: Tell the cops you did all in your power to ensure that the information was genuine but that you can only do so much.
Then provide all the info you have about the jerk (IP, email, etc...)

Option B: Go all out Snowden on them, claim your users have a right to privacy. That they should fuck off and come back with a warrant because you are a defender of internet freedom.

Note: Option B might get you to jail.