Hunting critters are smart: My experience is that raccoons get into a bloodlust, kill EVERYTHING biting off the heads, and then half eating one. Lost 25 bantams one night that way, its been war ever since.
If the blood is gone, then its definitely a weasel, they can't carry the body outside like a coon or fox will. A female fox will steal one or two and come back the next night for more. My uncle had a weasel living UNDER his chickenhouse, and didn't touch one of his birds but killed all the neighbours birds.
A tame city coon, might not even attack your chickens, they are garbage can eaters and take anything they can without a fight.
Living near a creek we always had coons trying to get my birds. For 10 years I tied one dog to the chicken house and left the other run free. I also "drained my potatoes" at different posts around my bird yard to leave a serious human scent. (I wouldn't suggest that in the city, then your neighbours would really have something to complain about.)