Plot hole: Early in the movie, when Joe Stefanos tells Mary, the owner of the luncheonette, that he found Jeff Bailey by passing by and seeing the name on the sign of the gas station, it makes no sense. He only knew him by the name Jeff Markham. Even if he was just lying to her, he uses the same explanation when he is alone talking to Jeff. We never know how he found him.
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Suggested correction: He told Jeff that he saw him pumping gas at the station.