He doesn't. If you read the book or watched either of the two movie versions of the story you would know that Ralph played no part in the murder of Piggy.
Ralph does not kill Piggy in William Golding's novel "Lord of the Flies." Piggy is killed when Roger, another boy on the island, pushes a rock onto him, causing him to fall to his death. Ralph is not directly involved in Piggy's death.
He throws a bolder on top of piggy
Ralph wants to get Piggy's specs back and Piggy wanted to kill Jack there and then.
Jack orders the boys to kill Piggy and Ralf.
to kill the pig
Piggy is Ralph's best ally but he does not stand up for Piggy.
Ralph is obviously the leader and Piggy is a followers, he likes to please Ralph. Ralph is also stronger and smarter, unlike Piggy. ..... Poor Piggy
he keeps on saying piggy piggy and he lets jack and the other know his name and they teases him about it
Piggy & Ralph
Piggy and Ralph are both characters in Lord of the Flies. The problem with Piggy and Ralph's plane is that it goes down and there are no grown-ups around to care for them.
piggy's glasses
Piggy.
Ralph's reaction to Piggy's nickname of "Piggy" is surprising because he initially scolds Piggy for revealing his real name, and later adopts the same nickname himself. This shows Ralph's shift in attitude towards Piggy and his acceptance of him as a friend.
Ralph and Piggy use a conch shell to call the boys together.