I feel your pain!! We've lost NINE of ten chickens since August of last year to savage attacks. Only one was a hawk attack. We free-range on our five acres and have two German Shepherds patrolling the area. We mistakenly thought (not accused, whew!) our neighbor's (both new) dogs since we found one survivor on the far side of their property after one attack that killed four girls. The following week we actually sited a coyote taking one of our two remaining girls right in FRONT OF OUR PORCH! Those critters are FAST! Our remaining Australorp, Hildy, is actually living part of the time in our house

. She's all alone and is a VERY social chicken!
We know that since this coyote has come back repeatedly, he/she knows that there's chicken on the menu. Therefore, my daughter's boyfriend is going hunting. I'm not a big fan of killing, but, I'm not raising chicks to feed the wildlife!
BTW- the coyote always shows up on the evening that our youngest GS is at S&R class.
Our 12 y.o. GS couldn't catch a coyote if her life depended on it, lol!
Our coop is very secure, and we haven't had any issues with 'something' trying to breach it.
Late afternoon, early evening, and early morning are the most dangerous times for our feathered friends. Vigilance, vigilance, vigilance; and even then there are no guarantees that something won't 'get' them.
I'm sorry for your loss, it's heartbreaking to lose chickens after watching them grow up, discovering their personalities, and becoming attached to them.