i just stumbled across this thread and read all 8 pages! i am soooo sorry for your loss! but i would believe the man that said it was the snake...
we had just put our 3 six week old babies out in a sectioned off portion of the outdoor coop (and this coop is very secure!) and when my fiance went out to check them in the morning, he found a 7' long black snake that had fully eaten our SIX WEEK OLD RIR BABY! i mean, this was no small bantam, but an almost fully feathered Rhode Island Red! The snake had also killed our Golden Sebright bantam and was about to kill our Black Australorp Bantam. My fiance killed the snake. (What was even sadder, is that our Golden Sebright had tried to fight back. She had pecked a couple of bloody holes in the snake!)
long story short, we found TWO HOLES in the coop, no bigger than 3/4". We searched and searched that coop for ANYTHING else. and it had to have been one of those holes that was smaller than an inch. this snake was VERY big too.
I would assume that what got your chicks was a snake.
I am VERY sorry for your loss though, I know how hard it is.