You are correct in surmising that it was a raptor.
The raptor killed chickens in have had they didnt cary them off they ate them in place. They flew off the kill and meal when I walked up.
I watched a bald eagle hit a malard once. When it flew off with it it could not get much altitude only 10 feet above the water and eventually dropped the duck. So im betting a chicken would be to heavy to pack off far if at all for most birds that are smaller than an eagle. Then two gone not just one at once. I lost multiple chickens to raptors but it was over several days.
My bet is on a fox with pups to feed. Fox will grab one and smash it for later and come back for more. I lost several ducks in one night to a fox.
Next guess would be dogs. But domestic would likely leave a mess behind.
I may be wrong but around here hawlks eat at the kill sight at least the few times I have 100% sure saw it, and also when oi come up on the sign of opend up eating chicken with bird poo on the ground at the kill.
Then again I had a crow foot and feathers all around a coyot set once. Remade the set and had a great horned own in the set the next day. So my conclusion was the crow wondering into my set. The owl carried off the crow and came back for 2nds the next night. It was a very cool bird I has no idea thair legs were so thick. Owl didnt even loose a feather and didnt even seem inconvenienced as it flew away upon release.
So an out can carry off a crow so I guess raptors could a chicken thats heavier.
Then again I could be wrong and anything else could have got the crow the night before and the owl was just attracted by the feathers spread around.
My first guess is still a nursing fox.