Yikes! That is terrible! I'm sorry for your losses...
And you've struck new fear in me now. I agree, I did not know that a hawk would wipe out a flock, rather, I thought they would snatch them off one at a time (I've had that happen...where every few days I have one less bird ).
To give myself pace of mind, and increase flock safety ... I have my chickens in with my goats now - and the goats definitely "protect" the chickens. I also purchased my first rooster (I've read stories on here about a roo sacrificing himself to a predator for the whole flock - not that I was him to die either, of course!), and I also have lots of hiding places for my birds in their run.
I'm terrified of airborne predation because my run is too big to net!
Again, so sorry the hawk took out so many. I'm glad you caught him red-handed though...knowledge is power!