Dogs break into coops and kill chickens all the time. Haven't you read about it here on this website?
Also, it wasn't a hungry animal because the animal didn't eat the chickens. Maybe it was a dog with rabies. Who knows.
A moose? Come on.
It may have been a dog that killed your chickens. Did you see any bite marks on the door covering the nesting boxes? Do you have any pictures?
I don't think a fox is strong enough to roll over a railroad tie and rip off a door covering the nesting boxes.
As mentioned, chicken wire does not...