I cracked open one of the eggs!

[Ks1063]

My Buff Orpington has been sitting for 24 days. About 2 weeks in, she got off the nest. There was some yolk on a few of the eggs, but I didn't find any shells broken. The eggs smelled bad, so I thought it was because of the exposed yolk. Yesterday, day 23, I broke one of the eggs only to find a fully developed chick with a small yolk attached! It was not moving, and I haven't heard anything from any of the eggs. I looked up pics of development. I would guess this chick was on day 18 or 19. I've candled the eggs, and most are solid black inside. My question is was this chick already dead, or did I kill it? I feel terrible. If it was alive when I cracked it, would there have been movement?