This thing was a living chainsaw! You're right that it was not like any cat I've ever seen. It may have been diseased or it was just plain crazy but either one would explain why someone got rid of it.
I had a feral cat have its litter beside my garage. My neighbor wanted me to take the litter to the vet. I offer the litter up to them but had no takers.
I made hte mistake of giving the cat water and food. The next day the cat attacked me. It ended up moving its litter off into the trees someplace.
I know for a fact that mink and weasels, etc., behave that way. I worked for a milling plant during college, and witnessed two mink enter the milling plant, while the machines were spinning and we were working. The mink worked their way through the plant killing any rat they flushed or caught in the open. We saw them go into rat holes and rats come running out, which were then run down and killed. It was fascinating. Any rat who attempted to make a stand, was quickly overtaken and killed with a bite to the back of the neck. They were one power team!!