Who was Mc Murdo

During this “story within a story," we learn that Douglas once bore the name “Jack McMurdo," and that he was part of a notorious gang in the United States, which was not unlike the Mafia. At the end of Part II, however, we learn that “McMurdo” is really a Pinkerton detective named “Birdy Edwards."

McMurdo was BirdyEdward Pinkertons man who work as a detective