If you are really concerned that you might have a predator, you can pickup a motion detecting light and focus it on your coop area. This can sometimes give you a chance to see what it is if you can view your coop the moment the light comes on. But they probably won't stay too long after that light comes on! I also noticed that several farming supply stores are now offering devices that come on when it starts getting dark and then turns off in the day light.
These devices emit either one or two red lites that go off and then back on all on their own and will last for up to 3 years. The predators that come by your area in theory, will take off when they see these red lights, mistaking them for another predator.
Check out the "Solar nite eyes" at flemingoutdoors.com, or the "Nite Guard Solar" at randallburkey.com
I have not tried them myself and they cost around $20 each. If your handy with soldering and electronics, you can find similar kits that you can build for $10 or less at canakit.com called a jumbo led or their mini 2 LED Blinker.
Just a suggestion.
Rolls