Piggy's death

How does his death contribute to the symbolism of the boys' descent toward savagery ?

Roger rolls a rock down the hill killing Piggy, in fact on purpose. Long before Piggy's death Roger, "picked up a stone, aimed, and threw it at Henry- threw it to miss" (p.78, l. 8). He threw the stone, but he knew that it was wrong. That's why he "threw to miss" (p.78,l.9). But living in the wilderness made him lose the feeling that it's wrong to hurt and also kill someone on purpose. He doesn't feel bad for killing someone any more. Losing that feeling made him a unpredictable, barbaric person. These are characteristics of a person that lives in total savagery. So the murder of Piggy shows that the inhibition threshold of the boys falls extremely.