Rick, I just started reading this thread this morning, but as soon as I read your description, I knew the killer was a human animal, just as Dan said. I'm a wildlife biologist by education, and as has been said earlier, a cat kill would have been very messy, and bears have no reason to kill a dog who is chained up.
I am an animal lover. My two dogs might as well be my kids. They live in the house, and have free run of the house. Even though I live in farm country, my dogs are only outside when they are on a leash. No matter how well trained, something could distract any dog enough for them to chase something in a road and get hit by a car. My house is maybe 1000 ft from the road, and the dogs could cover that distance in seconds and be hit.
I just contracted to fence a large area for them to play in outside. Even then, they will only be outside in their pen when someone is home, and then only for short times. My dogs weigh about 170 lbs each, so their pen will let them roughhouse all they want without wrecking the house.
I think you're right about neglect, and I agree with the earlier ideas of either trying to get a fenced area put in, or better yet trying to get the remaining dogs away from them and finding them the loving homes they deserve!
So many families in my area let their dogs run free, and they all eventually end up getting hit by cars or getting shot when they chase deer. Owning an animal is a responsibility, and it really burns me up when people don't take care of their animals.
In this case though, there is a real case of animal abuse, but it will be hard to prove who killed the dog, although I'm sure you have your suspisions. It's nice to see how concerned you, and everyone else in this thread, about animals!
Rich