If you're going to do this, why not use PM or phones to give the details of where and when anything that might happen, then the cops may know it's likely to happen, but won't know when or where and can't stop it...
But be very careful because they will know 'who' so you have to make sure no trace is left for them to pin it on you... They need more proof than a forum thread to convict you, but it certainly helps with the evidence trail and they'll know exactly who to start investigating...
That's my 2c (and advice). Someone please PM me to let me know what happens though - I'm particularly interested in the outcome now...