I didn't see any fur or tracks. Nothing to give me any clues. We live on a big, flat, open valley with brush, no woods. Lots of coyotes. Plenty of loose dogs.
This did happen several years back, but putting some wet sand down when I get my new chooks out there (different set-up) to catch any tracks is a great idea. Until I get my game cam.
Another reason I am leaning toward dog is that we had been out here for 7+ months without so much as a sniff from any predators. And now that I'm on BYC and know better, I am ashamed to say that for several months I had my hens in a dog crate inside the chain link cube, thinking they were safe. No fencing anywhere on the property, coyotes passing by night and day, and no attacks. So when this happened, I figured it was stray dogs. Although... don't dogs usually just kill for the thrill and leave the bodies? I never found any trace of my hens other than feathers, one part of a leg inside the hen house, and a skull months later that a packrat had hidden away in its nest that we found and destroyed (the nest).
The thought did cross my mind that human animals had bent the fencing and let their dogs in for sport.
Thanks for all the ideas. It was a horrible and hard lesson, but I learned it very well and my new chicks will benefit. I basically view any potential predator as a Tasmanian devil with uber strength and cunning with a side dressing of tenacity.