Call the police. If he confessed to your mom, he's certainly going to confess under their grilling. This is definitely harassment. Take pictures of the trash all over the lawn and pumpkin, etc to show evidence of the physical destruction.

I saw really inexpensive cameras with sensor control at Sams Club. I thought of getting it myself when our cars were being egged last year (never did figure out who it was ) It was under $100 at the time. I'm sure it doesn't take the greatest images at that price, but its at least something and something is better than nothing.