You have a prima facie case in that nobody should have entered your car and moved it.
But at the end of the day how much time, effort and money would you have to put into sueing? Versus how much justice and satisfaction would you get? Is the result worth the effort? You would need to keep your anger maintained for a prolonged period of time to see this through court. Do we HAVE to sue on every single issue where life doesnt treat us right?
How about moving your kid to a different school?
Plus, your son is not coming to law with completely clean hands on this. In England if you leave your keys in the car and it gets stolen the insuance company will not pay up. I wonder why? You are REAL lucky the car did not get stolen.
What if one of his school buddies had moved it as a joke? Would you be as keen to sue them? Or is it that you know the school has money to cough up?
And, although its not an argument, the officer does have a point. If everyone else had taken the letter of the law against your son he might well be in prison.
I work in a school and i find that the most badly behaved students (now im just talking in general, not about your son here) are the ones who DEMAND justice to be done to everyone else over the smallest issues. I am dealing with a case right now, of an extremely disruptive and rude student who drove a girl to distraction by calling her names until she flicked him with a ruler. Now his mum is demanding that this girl (Who is normally very quiet and studious) be expelled. She is not willing to accept that the girl was punished and made to apologise. And yet her son was caught making racist comments only yesterday, as well as smoking, being rude to me today and fighting another student during class. Sigh. Not everyone in schools are assholes.