In the episode "The Last Recruit," the Man in Black reveals to Jack that he had been impersonating as his father in a similar way to how he now impersonates Locke and how he impersonated Mr. Eko's brother, Yemi, revealing that at least some, if not all of Christian's appearances on the island post-death were the Man in Black.
Miles shows Sawyer a surveillance image, which shows Sayid Jarrah (Naveen Andrews) leaving the scene.
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