It could be a oppsum, coon or weasel---when i first got my guineas i had them in a trianlge pins on the ground they were made of chicken wire. And one morning i went out there and there was a beak laying there i looked and sure enough on of my keets dead and then i looked a little harder and saw it also ripped the head off of 2 and just left them there, which i was lucky all i had blocking the opening in the cage was a cardboard box and it could have knock it down and got them all. but it didn't. So i moved all my guineas in to our stock trailer. they were fine for 2 days them the next morning i went out and 5 more killed. But it left 4 in the cage and it opened the door. And the walls on our trailer are over 5ft high. it managed to get in and out. I suppose what was etting mine is getting yours. What ever was getting mine took their head through and ripped off what they could. And the only one who faced death that live got her whole wing ripped off and it was terribly infected. I am asumming a coons mouth isn't too clean eating road kill. Looked justlike that, i put proxide on it to kill infection then until feathers grew back i but sav on it and wrapped it everyday. I understand can't do that to a face, but still. Anyways i hope you find what's getting your chickens.