I haven't been able to keep up with the conversations completely, I take it you're convinced it was the hawk? The chickens I've lost to hawks generally leave nothing behind but a few feathers. However, my chickens are usually snatched when they are out in a more open area, where it is easier for the hawk to carry them off. Many hawks rely on striking their prey so hard they are knocked silly, and unable to escape, then carry them away. I can see how if if was the hawk, and hitting it by the coop it may not have been easy to get away with it.
Still, that type of damage also looks similar to what a possum, small dog, cat, etc might do.
In regard to ending the hawk menace, unless you are in a very isolated area, I'm sure the risk of killing the hawk is not wise. Never wise to fool with the Feds. In my state, the state statutes specifically mention that a person may kill predators that threaten livestock. What's unclear is how that would be applied if you were caught.
My chickens run loose all day. I'll loose a couple every year to hawks, and just live with it. "Life on the farm". Some things that I THINK might keep my losses down are:
Radio. I keep a radio going in the barn a lot. Does it help? Who knows, but I like the guys on the sports channel.
Fake Owls: I have two of these near the garden that I move around
Dogs: These help for sure. I've got 3 dogs that are out and about a lot. One is a German Shepherd that will chase anything, including birds, but leaves the chickens alone.
Cover and concealment: The hens are not dumb. They know the sound of hawks, and keep close to trees, trailers, tractors, etc to run under.
Nothing new. I'd try to make the hawk feel unwelcome. Noise, fireworks, water hose, wind chimes. Keep the hens in a pen until it relocates. Good luck; I know its frustrating.