You dont list where you are located, but if i had that result here in northern michigan with those tracks i would almost be sure i had a mink or martin.
Your unwelcome guest will return tonight for more fun. Take a whole chicken or a bloody piece of one that he killed and wire it to the trip pan, or in the back of a have a heart trap. It depends on what type of trap you have. Some have trip doors on each end, others one trip door. If you have to go buy one or borrow from a friend or neighbor, do so. Make it the medium size for racoon. Test fire it several times to make sure its not hanging up. Put it right in the coop where the chickens were.
Only trap this animal of you are prepared to kill it. You can not relocate as you will only give your problem to another chicken owner.
I am sorry for your loss!5
Last fall a weasel (a small cousin in the mink, martin family) found a way into my coop at night. A coop that i thought was impurvious to preditors. He killed my broody hen, all of her chicks and 2 other adult birds. The next night i caught him by wireing one of the dead baby chicks to the pan of a small have a heart trap. Its almost a sure thing your ermine will return.
Here is my weasel the next morning.
View attachment 1633577
Did you kill it? How?