Re: They're fighting back.
Your cat may not have met a bad end. Often, a lost cat is simply adopted into a new family. In an article I found on adopting stray cats, it said that almost half of cat owners adopted their cat as a "stray."
Make sure your current cats are tagged, or implanted with chips. This will at least help protect them if they ever end up in a pound (animals are always checked for chips). I know collars on cats are a supreme pain.