Actually Andy, you are not 100% correct. A fox killed one of our cats one very harsh snowy winter and carried it off. What's more the fox came back for the other cat a few nights later (fortunately, we rescued it from the fox!) We can only assume that she/he had cubs to feed and was desparate. Admittedly the cat was old and frail and I would agree that it is an unusual occurence.
However, pistolday, a fox would not remove a cat from a garden and return it a few days later. It sounds as if someone is covering up here. I am sorry this has happened.