Yeah, pointing out that they don't know the law isn't going to get you let off with a warning - ever.
Maybe you should have just let him continue operating in ignorance and then when he does arrest someone on false pretenses they can sue him and his department. THAT kind of black eye is a lesson that he would be unlikely to forget.
Maybe you should have just let him continue operating in ignorance and then when he does arrest someone on false pretenses they can sue him and his department. THAT kind of black eye is a lesson that he would be unlikely to forget.