How did they gain access to your coop? We moved to the woods and I'm trying to make sure my coop stays secure. Was there a door it was able to open? Was there no door but they got through a run?
It has usually been when I was unable to get home by dusk to lock them up.
On one occasion with meat birds in a grow out coop and pen an opossum was able to squeeze in and kill a bird.
I also had chicks in my cellar that were a couple days old and raccoons broke in and killed them all.
I've had good luck with hasps latched with carabiners about 4' above the ground.
There have been nights both of us were convinced the others put the chickens up. They start to roost around dusk but there's always one little bugger that bolts out the door if I try to put them up at that time. May try putting them up before it's completely dark.