Thank you for your entertaining peace. Having volunteered on Homesteads and building a couple coups myself, I am inclined to believe it's murder by jealousy. It's too late now, but there's always a jealous spinster in the bunch. You usually witness it if any of your birds have an evil nature. We had one hen that was such a rebel, she would peck all the eggs, so they were unusable. She knew exactly what she was doing, lol.
There is usually at least one outcast that gets bullied. Have you come to any conclusions?