"Hey man, I don't blame you for being upset. I WOULD call the Game Warden. Have them come out, explain what happened, take them to the spot where the trespassers were at. Allow the game warden to stay there and catch them in the act. They are most likely to come back to the same spot. "
Please call your county Game Warden and notify them of what is happening. It's now in YOUR hands to have this stopped. If they have done this once, they will do it again.