Pulling them through at that height is a bit puzzling. A raccoon , at that height, would only be able to pull something dead and would've had to been passed up from the ground. Which isn't possible from the outside of the pen because of the safety barrier. So if a coon is the culprit it would have had to of gotten inside the pen to do so. I've seen juveniles get their heads stuck in chain link fences before, so it could be possible for a young raccoon to slip through a 2x4in welded wire, but would have to go head first. Sooo, I would say a single raccoon would not be able to do this alone. All this being said, the same would go for a opossum. So, the trapper heritage in me is almost certain you very well could have a mink or weasel being your thief. And those are the devil to catch, but possible.