In Edgar Allan Poe's short story "The Cask of Amontillado" the narrator, Montresor, is clearly a sociopath. He is a cold-blooded killer whose only reason for murdering Fortunato is because of an "insult." He has absolutely no hesitation or remorse in carrying out the diabolical deed of walling up a man in the catacombs below his house.
In the first paragraph, he reveals his deranged thinking. He says that he must commit this crime so that no one figures it out but that the victim should know exactly who murdered him. Montresor says,
At length I would be avenged; this was a point definitely, settled --but the very definitiveness with which it was resolved precluded the idea of risk. I must not only punish but punish with impunity. A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong.
Indeed, the crime is never discovered. It is perfect in its sinister nature and could only be carried out by a man who felt no empathy for his fellow man. Even at the end when Montresor says for a split second that his "heart grew sick" we quickly learn it is not out of guilt but because he is cold.