what prey bird killed my chicken

looking for some advice from people more knowledgeable than me.

this morning i found 2 of my chickens dead near the door of their coop. it's possible the automatic door did not close last night so this could have happened any time after late evening yesterday. one of the birds was a 5ish kg cockerel who was always up for a fight.

cockerel was intact apart from having his neck eaten to the bone. head was still attached. hen had the start of the neck being eaten. 6 other hens are untouched. no sign of the usual "circle of feathers" you see with prey birds

everything i can find so far mentions mink, weasel, or owl. we do have weasel, pine marten, and possibly mink around, but the birds are in an electrified run and i see no digging or damage so i figure it must be some bird of prey. we regularly see buzzard and the odd kite but nothing bigger. 

the only thing that i can think is if we have a Eurasian eagle own passing by or in the woods surrounding the house but that seems pretty unlikely.

any other ideas 

thanks