Im curious to know how you knew the breed, as well. Just wondering.
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Some random thoughts....
If the unskinned head remained, and the pelt was gone, then almost for sure it was done for that pelt. While skinning a dog is not a crime that I know of, stealing a dog is.
If it was done on the property without owners consent, then trespass with malice is certainly a possibility.
If the person who did it is also the owner of the dog or the property, or connected, then a case might be made for something like animal cruelty, as well.
I'm thinking there cannot be too many Great Pyrs in your neck of the woods, either. It's not exactly a common breed out there in Salley, at least not among the locals. Makes me think the dog originated with some transplant folks. Likewise the perpetrator, you know?
It could have been a captured animal from elsewhere and that was just a handy spot to do the dirty deed. You could determine that better than any of us.
However, most such acts aren't random. A few, perhaps, but the odds don't favor it. It's highly likely the dog was local and the perpetrator is as well. Shouldn't be too hard to track down the owner of a GP in Salley, SC.
I say all that to say this: I tend to agree, too, that this isn't the end of it, but only the beginning. It could simply be some sick-a** redneck hunter crap. Something like young men full of themselves, etc.
But you gotta be pretty determined to skin a large dog. It may be a sign that something, or someone, far worse has moved into the area.
I'm not normally one for calling the sheriff, but in this case I would suggest it. Well, that and holstering up the .357 while out and about on your porperty.