It could be a number of things, depending on where you are. it sounds very much like a raccoon though, especially if you caught one near by. I know how you feel, yesterday morning the 2 rouen ducks I take care of for a friend where missing, and I found one laying in the grass, the entrails had been eaten but the rest of the body was untouched. We have a family of raccoons living in our woods, so that's probably what killed them.