This evening when I went to feed them, I found my 5mo old barred rock pullet dead. When I went in to take her out I saw that the other had pretty well eaten her from the chest up. She was completely healthy. I moved her and her sibling into the coop about a month ago, before that they were in a tractor next to the run, with chicken wire separating, and I would let those two out to free range along with the rest of the flock. So they were all pretty use to eachother. In that coop I have a small rooster, a year old hen, the two 5mo old barred rocks, and three 4mo old chicks. I usually let them out to free range, though not always, and there never seems to be any excessive fighting, today I didn't let them out. There was no signs of an outside predator, I haven't had one get into the coop or run yet. All the others seemed fine too. Could this have been the rooster trying to mate her too early and drawing blood, which attracted the rest of them to her?