I had a similar situation a few years back. My window was broken and door beat up. I knew who did it too. The cop said that since HE had not seen the guy do it, he could only take a report. My reply was that since HE would not see ME beat the hell outa this guy, that he would only be able to take a report when it happened. He agreed and a few days later, another dent got put in the bedside. This time it was his head.
I hate a vandal. Sadly enough, when the acts are completely random like that, it's often some kids with nothing else to do.