Cannibalism or something more?

Hello friends, I have a serious case that gave me a big scare today when I got home this afternoon. I went to check on my hens, and they were all chattering like usual and being their normal selves, but then I found one of them in the snow surrounded by blood and feathers. It looked like someone had a pillow fight that progressed into a full out brawl! When I went over to inspect her, I could see that all the feathers and skin had been ripped from her neck and most of her left breast was missing or had been somewhere next to her. I only wonder if this could be cannibalism because I had recently dealt with a serious case of pecking, so I thought maybe the hens could have gone after the same girl again?

Do chickens attack each other to the extent of ripping each other's throats out and flesh from their body? Or could it something else like a hawk? It's winter right now, so food for hawks could be at a very low rate for them right now, but it's always easy for them to go after defenseless chickens. The only thing I see wrong with this is that we have heavy duty fishing line over the top of our run (meant specifically to block hawks) and it didn't look like something had forced it's way through. Would a hawk be able to squeeze through, if that's something that they even do? I'm very sad about my hen's death, but curious about it so I can prevent myself from coming home to another murder scene.

If anyone has any suggestions or thoughts, I'd be happy to give them a read! Thanks!

 

Oh gosh! This is the first time I've actually had this happen. I can't just seal my hens up in the coop forever. What do I do to prevent it from killing another?