Jack's answer to Stanley's question is another example of his evolving and growing ability to channel the boys' fear to strengthen his position of leadership. Stanley cannot even finish the question but brings up the idea that it was actually Simon they killed in their frenzy on the beach. Jack counters that it was in fact the beast that they killed. Instead of focus on any discussion of it, he moves on to urge them to continue the practice of leaving any heads of kills to the beast in order to stay on its good side. In doing so, he makes it possible for the boys' fear to continue to drive them to trust him despite their misgivings.
It stands in stark contrast to the discussion that Ralph and Piggy have about the incident where Ralph clearly comes to understand the part they played in the murder. Ralph even goes so far as to admit that he is frightened of himself, of all the boys and what is inside of them. They try to justify it and comfort themselves by saying they were at the edge of it, but it is clear they understand they played a role in killing Simon. They make no mention of him being the beast.
Jack and the other boys in his camp, are becoming more in danger of madness. We see how Jack is keeping them worked up about the beast on the island. When all the boys see Simon, they jump on him and kill him. Ralph and Piggy are the only ones who feel bad about what they have done. Jack tries to keep control over the boys, by telling them that was the beast and they had no choice but to kill him. He tells them that the beast is still out there and will disguise itself as anyone, so they must always be on guard against it.
When they take Simon's body out to sea, we are seeing that Simon was the innocent one on the island. He lived in reality and wasn't swayed by Jack's antics.
"Surrounded by a fringe of inquisitive bright creatures, itself was a silver shape beneath the steadfast constellations, Simon's dead body moved out toward the open sea."
This quotes shows us how special Simon was. He was an innocent victim of the boy's madness burning within them.
Jack convinces the boys (and arguably himself) that it was the beast they killed, which was their first reaction upon seeing Simon due to mob mentality. Even though Ralph and Piggy admit to each other they knew it was Simon, Jack perpetuates the myth of the beast on his side of the island. This is arguably because in keeping fear of the unknown alive on the island, Jack is better able to lead in a totalitarian-like way. He convinces the boys that even though that night they thought they had killed the beast, that they actually hadn't - that they actually couldn't - and he suggests leaving sacrifices for it instead.
- Jack convinces his tribe that Simon was the beast; he also kept the fear on the island by introducing the idea that there are many other beasts still present. He explained that the beast comes in many different forms and is ultimately indestructible. By keeping fear intact on the island, he gets to keep and enforce his absolute power.