Sounds to me like a racoon. I found this info online for you.
"Parts Missing
A dead bird found inside a fenced enclosure or pen with its head missing is likely the victim of a raccoon that reached in, grabbed the bird, and pulled its head through the wire. Or a bird of prey could have frightened your birds into fluttering against the wire, and those that poked their heads through the wire lost their heads.
When you find a bird dead inside an enclosure with its head and crop missing, your visitor was a raccoon. If the head and back of the neck are missing, suspect a weasel or mink. If the head and neck are missing, and feathers are scattered near a fence post, the likely perp is a great horned owl.
Just as a raccoon will reach into a pen and pull off a chicken's head, so will it also pull off a leg, if that's what it gets hold of first. Dogs, too, may prowl underneath a raised pen, bite at protruding feet, and pull off legs."