Hi, so sorry for your loss, i know there are a lot of mixed replies, on what done this.
However it sounds like it was a fox. Especially if you have seen one, hanging around.
Like the saying goes, (SLY AS A FOX) and boy they are sly, also clever and very daring.
If they are out for food, to feed their cubs, then day/night if they see the chance, they will
risk it. A fox wiped 16 of ours out, only because i had not locked them up, this one night. Although we live in UK in a small village, i bred them 7yrs before, did not even know we had foxes. We learn"t the hard way. He got over a 6ft wall, it was horrific to
see. But where my girls were heavy, he could not get them back over. They were everywhere, even in the coop, he left them all over the place. Every night for 7yr
i locked their coops, bar for that one night. It was heartbreaking to see. We have all been there, on here. Like i said, the only threat we have are foxes, here. I hope you get
the blighter. Is there a way, you can move your coop, to a place, where you can build
a run. Even though it is only foxes we have, our new coop + run, has also an enclosed roof. Plus, i lock their coops every night, As i never ever want to go through that again.
My heart goes out to you, and i hope you sort it.