I agree with Flint. Let him know that you saw him. You may even want to tell him that at this time you want to be a good neighbor and NOT turn him in. Also mention that this will be the only time that you WON'T call the Sheriff. Next time you turn him in. That may be all the warning he needs. If you turn him in now I would guess you could find some stands missing. Remember you will still be neighbors with this guy.