What he did was clearly outside societal norms...so much so that I think it's worth looking at the motive. Granted, the most likely explanation is that he's twisted, but that's not the only possible explanation (given the article info). Although some later postings seem to indicate such is not the case, one possibility that immediately presented itself is that he was butchering it to eat. Not everybody hunts or farms, and in a society where meat is something people get in a supermarket package the ethos and skills needed to cleanly and humanely harvest one's meals is largely absent. Hunger also drives people to desparation.
Again, while later info strongly suggests such is not the case here, I suspect that if you placed the average American in a position where they had to kill their own food with only a knife, there would be very few clean and efficient kills.
"...given the eyewitness account (that you for some reason believe there may be reason to cast doubt on)..."
Much of my living is made by collecting and evaluating, "eyewitness accounts." There's a reason to cast doubt on everyone, and it's not that people are trying to intentionally dissemble or mislead, it's because no matter how hard one tries to be clinically objective, all our observations are filtered and interpreted through our biases and experience. Some people are better than others, but the simple matter of individual perspective makes it extremely difficult.
Again...I've never said I'm defending this guy or what he did, and to suggest I am is blatantly dishonest. His actions were not acceptable within the parameters of our society, but there may be more than one explanation for his deviation from them, particularly with the limited information in the article at the time I made my initial assertion.
How would you like it if I “amet” your dogs... on a platter in my kitchen?