At Ben's old house at the barracks, Ben leads Locke into the house and tells him that Charles Widmore and Zoe are inside and that Zoe is armed, but he assumes that doesn't matter dealing with smoke monster Locke. Locke tells Ben to wait outside because he doesn't need to see what's going to happen, but Ben says that he wants to see it.
As they Locke enters the room, he says to Widmore that it's nice being able to talk without the fences. He asks Zoe who she is and as she's answering, Widmore tells her not talk to him. Locke swiftly pulls out his knife and slits her throat. She falls to the floor, bleeding and quickly dies. Widmore asks him why he killed her and Locke says that since he told her not to talk to him, that made her pointless.
Locke then tells Widmore that if he doesn't tell him what he wants to know, then the first thing he'll do when he leaves the island is kill his daughter Penny. Widmore says that he'll kill her either way, but Locke gives him his word that he won't if he cooperates.
Widmore then tells him that he brought Desmond Hume back to the island as a "last resort," then says that he won't say anymore in front of Ben. Locke tells him to whisper it and as Widmore leans in a whispers, Ben fires three shots, killing Widmore. Ben says "He doesn’t get to save his daughter!" Locke says that Ben never ceases to amaze him and adds that Widmore had already told him what he needs to know. Ben says that's good and asks "Did you say there were some other people to kill?"
So Ben finally got what he wanted by killing Charles Widmore, apparently forgoing whatever rules they were playing by that were addressed in "The Shape of Things To Come" in season 4. Ben certainly seemed to let his jealousy surface again, making another rash decision. He certainly doesn't like the idea of Jacob talking to Widmore and not him. This jealousy is what led to Jacob's death.