Both Ralph and Piggy understand, at some level, what has happened to Simon. Ralph tells Piggy, "That was Simon . . . That was murder," and struggles to comprehend the enormity of their action. Unfortunately, reason is not Ralph's strength, and he can only rock back and forth, murmering, "I'm frightened. Of us. I want to go home. Oh God, I want to go home."
Piggy tries to rationalize the death by claiming that it was an accident, that they were scared, and that it was somehow Simon's fault: "He was batty. He asked for it."
If Ralph understands but can't accept, Piggy accepts but hides understanding under a cloak of denial.