In William Golding's Lord of the Flies, several deaths underscore his theme of savagery. A significant difference between the deaths is that the first two deaths--the death of the boy with the birthmark and of Simon--were an indirect consequence of the boys' nature, whereas Piggy's death and Ralph's near death were very intentional.
In Chapter 2 during the group's first meeting, a small boy with a "mulberry-colored birthmark" is urged to speak up by a group of similar small boys. It's through the boy with the birthmark that we first learn about the presence of the mysterious beast on the island. As the chapter progresses, Ralph encourages the group to build a fire to use as a signal, and all the boys run off to start building it on top of the mountain. Their attempts to build a strong enough and long-lasting fire are unsuccessful and lead to a series of quarrels in which Piggy protests no one has the right to speak because he holds the conch. Piggy soon notices that, during the quarel, the fire they had built had set fire to a section of the jungle, a fire they are powerless to put out. As they continue watching the jungle fire grow, Piggy realizes he doesn't see the boy with the mark on his face, causing all the boys to fall "silent as death" as they all face the realization that, while they were being quarrelsome and neglectful, one of the youngest boys died in the fire. The fact that the boy died was indeed a consequence of the boys' actions; however, it was only an indirect consequence because, at this point in the story, no one intended to kill anyone.
In contrast, in Chapter 10, just as Piggy is making a poignant speech about the need for rules, Roger very intentionally releases a bolder that murders Piggy. Roger is described as feeling a "sense of delirious abandonment" when he released the bolder, as if he felt ecstatically joyful about finally loosing himself to all of his evil urges.