ULPT Request: How to deal with a Mailbox Thief (Have License Plate)

 Live in Suburban Upstate NY. Since the summer I have seen an unmarked navy sedan that goes through people’s mailboxes in about a square mile radius probably 5 times. Each time is around 12:30 am and they pull over to the left side of the road and reach in and whenever they see me they wait for me to pass. 
 Now twice I have trailed them and I have the plate. What can/should I do to give them hell?