Three murdered and three survivors

When I went to put the chickens to bed last night none of them were in the hen house. After calling and searching, one bedraggled little hen called back to me, she was soaking wet and missing half her feathers but was alive, so I tucked her up in the safety of a nesting box.
There were a lot of white feathers everywhere, but I couldn't see into the undergrowth as it was getting dark. I didn't sleep very well, but this morning there was a chicken outside the kitchen window! I reunited it with the one I had rescued last night and resumed the search.
Sadly I found the dark grey and a white chicken in a small space behind a woodpile, both had lost their heads. There were feathers suggesting that the other white one had been dragged through the hedge and out towards the road, and there was no sign all of the pale grey.
I'm happy to have two survivors anyway.
UPDATE: 6 hours later!!
I went out to lunch and on my return found the missing white chicken had limped back into the garden, she wasn't in the chicken's enclosure but was desperate to get back into the safety of the hen house. I let the other two out at that point as they had dried out and perked up a lot, but white chicken has a large bite out of her back, so should I take her to the vet for antibiotics or see if she makes it through the night?
Then I found the headless body of the pale grey chicken, in a place I had searched last night and this morning!