Responses
I think the way Jin didn't technically kill him, makes he want him to experience the same hell he did rather than just a brief pain. I mean he quiet literally ask him to build a hell for him at the end there
Maybe he wasn't ready yet/was too indecisive: "maybe doing this is the perfect revenge! No, that's too simple compared to what I suffered... Oh, maybe-"
Its so insane how he did not kill Jin when he first met or locked his conscious up somewhere