In "The Life and Death of Jeremy Bentham," Ben saves Locke from killing himself only to kill him moments later. Why did he Ben save him, only to kill him again later? I have several theories. First, maybe Ben was also told John Locke needed to die. Second, maybe John would not let Ben tell Sun the truth about her husband being alive, as Locke promised he would tell Sun that his body washed up on shore so as to prevent her from coming back. Because of this, Ben needed to kill John. My final theory is that Ben didn't know Eloise was the person he needed to talk to in order to get back onto the island. Once he got this information from John, he allowed himself to kill Locke because he was threatened by John's "special" status.