So sorry about the loss to you and your neighbour! It must've been awful for the hens.
We have a jack russel mix terrier who we've trained to not mess with the hens. She and the rooster will have a staring match once in awhile and the hens will often chase the dog to let her know her place which I'm happy for them to do. But I would NEVER let her with the hens without supervision. We have made our run so that critters (foxes and dogs alike) would have trouble digging to get in. So far, so good.
A neighbour recently had a bantam game cockerel on his own which he fed one morning and then cockerel was fine. When he returned in the afternoon the cockerel was dead with his crop eaten through. He figured a rat killed it and ate through the crop for the seed! Poor cockerel! It must've been a desperate rat to go to that length of killing the bird for the seed!