Your roo looks slobbery on it's feathers between the neck and wings. I'm guessing a dog played with it. They'll carry it around, pounce on it, etc.. This can cause internal injury with bleeding out the mouth. Since the dog is only playing, they don't eat the body.
Raptors (hawks, owls) don't leave their prey on the ground. They don't hunt when they (or their chicks) aren't hungry.