Let your anger cool and then go have a sensible and non-accusatory convo with the parents. Don't come at them with your anger towards his son. Take the position that, of course he will be horrified too! Enlist him as an ally in bringing his son to "justice." It may or may not help, but it is the only constructive action you can take at this point.
You may be surprised and the Dad may make the son feel tangible consequences, or it could be that he tut-tuts with you but does nothing.
At least you will have taken the sole, legal action step open to you, and the son will at least probably never pull a similar stunt again.
Speak with the Dad as much to let go of some of your anger (but not directed at him) as for any other reason.
I know as soon as it happened I would have been on the Dad's doorstep showing him what had just happened and having that convo. Visuals can help immensely when telling someone something they'd rather not hear or deal with.