I have had hawk attacks, but this looks different. The body is found in a different place from the head, one time intestines were with the head, body 20 feet away. Sometimes the flesh is striped from the neck with the head still on, the body is never eaten, sometimes a big hole in the breast. Is that characteristic of any certain animal? Sorry so graphic, but I'm trying to figure out how to make my pen safer. I put them in their house at night.
Those are the tell tale signs of an ermine kill. They like to kill for sport, and will often only mutilate and nibble on their kills. I have had them take 5+ birds a night if they can get to them.
I have seen the same results left over from coons that broke into my folks' duck house at night when I was younger. Heads separated from bodies and necks gone. Woven wire perimeter fencing 6' tall with 2x2 squares is what I use. The same can be used over tops of runs if you have a good sturdy frame, or good quality 1" chicken wire. Any openings at the eaves of the coop's roof can be sealed well with .5" hardware cloth stapled around openings. Laying hardware cloth or fencing flat, around the perimeter of the yard discourages digging. Coons can climb, so trees trimmed away from the yard fencing and coop roof prevent a ladder for them. Electric fence around the perimeter of the yard is an option too. Get a dog sized, sturdy cage trap and bait it with cheap canned cat or dog food and leave it set at night. Population increases of coon and fox can become a real problem if numbers are not controlled. I'm not sure about laws in other states, but it is illegal to relocate wild animals here. With coons, it is not a good idea since they are so territorial/vicious with each other, and they often become a headache for someone else when relocated. A humane and quick way to remove them once trapped is a .22 shot to the head. Using 22 shorts are a less noisy round. Know the law about discharge of firearms in your area, and of course, safe use of them. Much can be answered by your local Fish and Game department.