Predators happen all the time. They are the top expense and worry of chicken keepers everywhere. Predators of all kinds - from coons and weasels to hawks and the neighbors' pets - are the reason we spend so much time and energy, not to mention money, on predator-proofing our coops and runs. And people think we're in it for the "free" eggs!
There are lots of things that could have killed your hens, but there are lot s of questions to ask before you can know. Are your chickens free-range? Were they in a coop or a run when they were killed? If they were, how predator proof is it?
Google "What Killed My Chicken?" There are some pretty specific details about what each type of predator leaves behind, right down to a description of feather patterns on the ground and which body parts are eaten or damaged ... or left untouched. For instance, dogs will leave a "blood bath" with feathers and bodies strewn everywhere. They kill just because those nifty chicken-toys are fun to chase, but no fun to play with once they're dead... so they move on to the next one.
Roosters don't generally kill their hens, and if the aftermath was that messy, he wouldnt come through the fight without considerable damage to himself. So, don't be too quick to blame your roo. If something else got your chickens, he may be what saved your last two hens!