Hi.
Thought I'd give you some info on what the police is allowed to do and not here in Sweden. Not sure this applies for the states however.
Police can and probably do watch sites like this one. However they are not allowed to "encourage" crimes. That menas that police can't post "I want to buy" or "Where can I find..." since this is considered "encouraging" crime. So getting an email from a cop who wants some gear is against the law and evidence is not ligit in a court. But sometimes even those bastards break the law. And once again this is Swedish law, and I'm not 100% sure it applies in USA, but I'll find out. I'll come back on that one, if noone else beats me to it.