The fact that he hides these details leads to believe that Fortunato was someone that he needed disposed of, so to speak, for a reason that we will never know.
The next case of the twisting of the story is that the narrator has a very sketchy way about him in the manner that he tells his story. We get a sense of the shady nature of the narrator very early in the story. First off, he has chosen a time to lure Fortunato into the catacombs while the whole city is in a state of festivities. Fortunato is dressed in a jester's costume, which helps to avoid the possibility of anyone recognizing who it is that he is leading into the underground tunnels. Also, since it is a time of festivities, everyone is inebriated, again helping avoid the chance of them being recognized. Second, he lures Fortunato into the catacombs by aiming at his "weak point," being that "he prided himself on his connoisseurship in wine" (165). Finally, while descending deeper into the tunnels, the narrator often stops to share more wine with Fortunato. He does his best to keep Fortunato intoxicated throughout their entire journey. For instance, " 'a draught of Medoc will do the trick'" and "I broke and reached him a flacon of De Grave. He emptied it at a breath" (167). All three of these examples show greatly the shady nature of our narrator, but due to Fortunato's intoxication he hides it well from him. .
Thirdly, though he hides it well from the man upon whom he will commit the murder, throughout the story Poe gives us many foreshadowing hints of the narrators plan. These hints are very subtle, and not picked up upon by Fortunato due to his inebriation. The first of these subtle hints comes when they make there first stop for a drink. "And the motto?' asks Fortunato about his family's coat of arms. "Nemo me impune lacessit," replies Montresor, which means "no one provokes me with impunity" (167).