From my experience with raccoons. If they have the opportunity they will not kill only one. And they won’t just decapitate. I was left with nothing but bones and a chicken with its leg ripped off because he could not pull it through. My mother-in-law‘s experience left her with no chickens. I feel like raccoons would’ve done much more damage than just decapitation . Whatever it was a game camera could really help. You might find stuff out there you didn’t even know you had aroundIt could have been a mink, weasel of one of the cousins. Except with those, they often kill a whole bunch of birds and not just one. So another possible culprit would be coons.
But if weasels, you may want to make a weasel box. A weasel is small enough to use a standard Victor wooden rat trap in your box. A mink is larger, and while you use the same sort of box, trap for a mink now becomes a body grip along the lines of a 110 or even 120. Box gets modified some to handle the springs.
You can google Weasel Box and Mink Box for ideas and instructions on how to build the box, set the traps and what baits to use. My only advice on the Mink box is to find something other than Duke body grip traps. The Dukes are mass marketed and easy to find, but are not as well built as others and the triggers not nearly as good as many of the others. Traps like BMI.
If coons (read that as plural, as in more than one) then use the dog proof traps. The DP traps cost about 1/4th what a good live trap runs and are more effective on coons. So for the same money, you can buy several and nab a bunch of coons on the same night.