It looks like dog to me. Everything points toward dog.
Regarding the missing carcasses: We've had that, too. The owners of the dogs must have taken them away. Once they started to rot and smell we found some but all the obvious ones were missing. We lost 18 chooks in one attack and had a dozen or so injured. It was very brazen of the owners to collect them.
No human rips bits of skin out. In our case we were able to see teeth marks in some of the injured chooks. The size of the jaw of the dog(s) was not much bigger than a tom cat's jaw.
Dog and ferret/stoat are the only perpetrators who kill everything they can get. Ferret kills have only got a bite wound in the neck area. Dogs grab what they can get, usually it's the tail or the back.
We've had 4 dog attacks over the years and in one case we saw it happen. There was nothing we could do as the dogs attacked hubby when he tried to chase them away with a spade. We called the police and they arrived within minutes. The dogs were still in a killing frenzy and tried to attack the policemen. They got their taser and fired it but missed. The dogs sensed that there was a weapon and jumped over a 6 foot fence with 4 people witnessing it. There were no chicken survivors
Animal control got involved and we were told that these dogs had left their property during the night without their owner's knowledge many times and had killed rabbits and other livestock during the nights. As we couldn't prove it was these particular dogs no action was taken but they spent the rest of their lives on a chain.
Eae - I'm sure your Barred Rock will be ok. Chickens heal very well and you won't even notice the scar.
Wolga - the only human involvement I could imagine would be a human with a dog who was trained to catch and bring prey so they might have used the dog to catch the birds alive. But this doesn't make sense to me. If I wanted to steal eae's chooks I'd sneak up at night and just take them off the perch, put them into a big sack and leave. Very few feathers would be lying around and I doubt a single chook would have left the coop before being put into the sack.
And no - I'm not planning to steal anyone's chooks - I've got too many myself already
