[daftpunk]

That's a tough situation. You should have probably stopped right away, confront them and threaten to call the cops on the spot for vandalism. Frankly the cops probably don't care now, and it's unlikely that that'd take action, especially with no proof. It's so easy for the lady and her husband to deny the whole thing.

Back in highschool, somebody I knew did the same thing (he was the aggressor)
threw a brick/large rock or something at a lady's car. She stopped, called the cops.
I think he was charged and was forced to do community service and take anger management classes. This was in canada though, lol.