So sorry to hear about your troubles with the dog; it's truly a shame when something like that happens.
It is a shame, and unless the dog has other issues, it's not ~necessarily~ even a bad dog, just an uncontrolled one. Every dog, bird dog and mutt alike, that I've ever owned would kill a chicken if they had a chance to. It's a natural thing for them to want to do, unless they are specifically trained not to, and even that doesn't always work. That's why dogs within range of neighbors have to be fenced.. their instincts can cause problems and grief for other people, as well as themselves.