Graphic photo - lost one of my girls yesterday

[chickengeorgeto]

Thank you all! I did keep the chickens in their run today, although a few of them can fly out...

If a chicken can fly out of the pen then a hawk or owl can fly in.

 

[dmanhefner]

Hawk. Owls eat then at dusk, night if they are uncovered and just before day break. Hawks make the feather bomb you have there, owls it will looks like someone cut pieces off your chicken with scissors. They usually eat the head, neck, and cut through the back to eat the heart lungs and liver. Owls usually don't do the feather bomb either.

 

[Shadrach]

The only predator that removes heads here are weasels. Apparently they like to feed the brains to their young. Hawks almost invariably pluck the lower neck and back and eat the internal organs leaving the head intact.
The other thing that makes me wonder if it was a hawk attack is you don't mention any alarm from the other chickens. Here the chickens all know about the hawks and in every case I've come across they all give the general panic call after the strike. This isn't always the case for ground predators.
Obviously I don't know what got your chickens but belly wounds and head missing makes me think weasel or similar.

 

[cmom]

What ever it was it will probably be back. If you have a game camera that will likely tell the story. Several years ago I was loosing some birds so I put out a game camera. It was an owl.