I had a similar experience years ago. We were back on our private ground before we built the house on it... hunting in the fields. 5 of us (Bros/dad/me) were loaded up in a truck driving across the fields when we spot a truck. We drive over and one brother confronts the driver as to why he is trespassing.
I recognized the voice and noticed it was a kid that I went to school with. The first words out of his mouth where "A buddy of mine from school said I could come out here". Being one to have a temper on occasion, I flipped my lid. I knew the kid somewhat, not friends-not enemies, but I certainly didn't give him any ideas about hunting on our property. I came flying out of the truck and screamed WHO GAVE YOU PERMISSION? His face turned white, he knew he was busted. My brothers detained me and let the kid go, just warning him not to trespass.
Two weeks later the lock was shot off our barn and 8-10 treestands were stolen from inside. We all had our suspicions and finally confirmed it was the same kid we had ran off just weeks before. We were livid! The cops checked his place out and couldn't find any of our property so there was no way to press charges.
That was a real kick in the teeth to be treated like that. Of course in the long run we came out alright... things have a way of working themselves out- here in the country.