I am so sorry about your loss. That would have been awful for your girls to find.
Whatever got to your chicken now knows where to get a free meal and will almost certainly be back. So, none of your other chickens are safe with the set up you have now.
Whenever we free range our chickens there is always the possibility (some will say probability) that a predator will take some. It's a risk that we each, individually, have to decide if we are willing to take. If not, then don't free range your chickens or only free range when you are there watching them.
It sounds like you do not lock your chickens up at night either. I'm amazed you haven't already lost some to nighttime predators. If you want to keep them safe they have to be securely locked inside at night.