The carrier arrived at Altoona to deliver one trailer and pick up another trailer. As he placed the trailer into a dock door he was able to see the nose of his return trailer out his side window which made him immediately recognize that something was wrong. When he approached the back of the trailer he noticed that it sat approximately 8 feet from the dock door and the trailer's roll door was halfway open. He then checked for a seal on the ground and did not see one. He noticed drag marks which he described as new and fresh. He checked the king pin lock and discovered it to be covered in grease with a piece of metal stuck to it which he identified as a 'tooth' from a tractor's fifth wheel. When he removed the king pin lock a piece of metal was broken off inside, but the king pin lock still worked. Photos of the site were taken. He then called his dispatcher and the gatehouse to report the situation. When the Store team reviewed the exterior dock area, they discovered a seal lying on the ground. Based on its return bill of lading, it appears that all product is present and in good order.