To what extent can the narrator be relied upon to give an accurate portrayal of events?

Although Montressor turns out to be a murderer in "The Cask of Amontillado," he nevertheless turns out to be an excellent storyteller. The story is told precisely and in a matter-of-fact way. Montressor makes no excuses, nor does he embellish the situation. He does not tell the reader what crime Fortunato has committed against him--perhaps Montressor's only fault in the retelling of his murder. The events seem perfectly logical, and Montressor's lack of remorse further magnifies his belief that he is committing a justifiable act. Of course, Montressor could be lying, and the whole story could be concocted. But if he tells the truth, and "for half of a century, no mortal has disturbed" the body, then the evidence still remains in place.