The white leghorn looking hen may have been killed by one predator then the carcass was scavenged by a separate predator. Question, is there a secure roof or top on this run? The likely hood of a dog jumping the fence makes me think that other varmints can also gain access to your birds from above. The hog wire or field fencing in your pen or run is an excellent barrier against which a predator of any description can pen or corner a panicked chicken. Indiana has a full compliment of flying, climbing, and jumping chicken thieves. The missing internal organs makes me want to blame a possum. The small under feathers plucked out and strewn over half of He&& and all of Georgia says owl or hawk to me. Because maw possums carry her brood either in their pouch or riding on her back means that mama possums don't carry morsels of food back to their young but raptors do because their young are nest bound for a couple of months. So maybe the head was dropped by a hawk or owl in route back to its nest.
If he carefully chooses his ground, a small coon can not only defeat a dog that is much larger, but kill the K9 as well.