From what I have seen hawks / falcons go for the intestines to get to the heart and liver. I've seen this happen at our bird feeders when a falcon would catch a morning dove or cardinal it would take it to a tree in the yard and go right for intestines and drop the rest to the ground for me to...
I would say hawk, a hawk will try to break the neck and then go for the guts. Was the neck broke? You did say a large white bird was seen there and they have a good memory on where there last meal came from.