Where does the exposition end and the movement toward the story’s climax begin? Where does the resolution stage begin?

The exposition could end in several places. However, once Homer disappears and the cousins come to visit briefly, I think the suspense begins to rise making us wonder what will be found eventually. The climax, I believe, is the discovery of the body because then, we know that "the end becomes the end." We are disgusted perhaps by the fact that she has rested beside the dead body, but we are not surprised once we realize she has killed him.