My first guess by the description is weasel... What state? (Alabama.. sorry) Just wonder what type of predators you may have. An Opossum will do that too.
IDENTIFICATION OF THE PROBLEM PREDATOR
The best long-term solution for protecting your flock is preventing predators from getting to it. Of course, this tactic is easier said than done. To develop an exclusion plan, you need to determine which type of animal is preying on your birds.
Often, the condition in which you find your flock is an indicator of which predator is involved.
If adult birds are missing but no other signs of disturbance exist, the predator probably is a dog, a coyote, a fox, a bobcat, a hawk, or an owl. These predators typically are able to kill, pick up, and carry off an adult chicken. Hawks typically take chickens during the day, whereas owls take them during the night.
If chicks are missing but no other signs of disturbance exist, the culprit may be a snake, a rat, a raccoon, or a house cat. Such predators sometimes leave some feathers and wings scattered away from the site because they are not able to swallow these parts.
If birds are dead but not eaten and have parts still intact, a weasel may have attacked the flock. Often the chickens’ bodies are bloodied. Also, you might notice that internal organs have been eaten.
If birds are dead and not eaten but are missing their heads, the predator may be a raccoon, a hawk, or an owl. Raccoons sometimes pull a bird’s head through the wires of an enclosure and then can eat only the head, leaving the majority of the body behind. Also, raccoons may work together, with one scaring the chickens to the far end of a pen and the other picking off the birds’ heads.
If birds are only wounded, not dead, various predators may be to blame. If birds show signs of bites all over, a dog may have attacked the flock. Dogs do not have sharp enough teeth to consume animals cleanly. If the wounds are on the breasts or legs of young birds, an opossum may be the problem. Bites on the hocks of young birds often indicate that rats have preyed on the flock. If birds have bites and show signs that their intestines have been removed through their cloacae, the attacker may be a member of the weasel family or cannibalism may be occurring in the flock.
If eggs are missing, one of several predators—including skunks, snakes, rats, opossums, raccoons, blue jays, and crows—may be at fault.
Welcome, and I'm so sorry for your birds! Any still alive?
So many different predators will be able to enter through 3" openings! Every opening needs to be no larger than 1/2" diameter, and latches need to be difficult for children to open, to prevent repeats of this horrible event.
Mary
I'd say skunk depends on location. I've heard a skunk will go for feed or eggs and just rip the head off of birds. As first comment said could be lots of predators. I had a gap I couldn't fit my hand through but watched a grown raccoon run through like the whole gate was gone. Probably had something to do with the first round that went into him.
And I am sorry for your loss. I lost 5 of 7 in one weekend and it is devastating.
Likely as not, that damage was done by coons. Even adult coons can get through some small spaces and half grown coons that are learning to hunt this time of year, even smaller. Coon predation is so bad this time of year, good rule of thumb is to assume it is coons until you find out otherwise.
Not likely OP has Minks (1 1/2" opening) or weasels (1").....but either of those would kill a lot of birds by severing back of neck at the base of the skull......and might even rip the heads off in doing so.......but seldom chow down on the necks and crops like that.