Hide and just stalk the responsible to his car, then ruin it when he s away in one month from now or smthg, scratch the doors/body side oposite of the driving seat so he cant see it when he leaves...someone will just tell him "hey what the fuck, have you seen this, this side of your car has been scratched"...
Will make a great xmas present. He ll never know if it's you but somewhat will be convinced it is, yet he wont be able to do shit against you.
IF, your bullshit story is true, of course.