As in other stories of his, Poe does not establish a precise relationship of the narrator/killer and his victim. This ambiguity serves to heighten the gothic suspense as the horrified reader wonders why the killer commits his action. In "Tell-Tale Heart," for instance, the narrator declares,
It is impossible to say how the idea first entered my brain....Passion there was none. I loved the old man. He had never wronged me. He had never given me insult. For his gold I had no desire. I think it was he eye! Yes! it was this!
Obviously, the narrator is well-acquainted with the old man. However, there are none of the "normal" motives here for murder. The motive seems to be generated by the obsessive "nervous" insanity of the narrator: He focuses on the "pale blue eye, with a film over it." As in the poem "The Raven" in which the narrator imagines that the bird itself has a sinister reason for persisting in the repetition of "Nevermore!" so the narrator here imagines that the eye itself is evil. Thus, the narrator himself creates the deadly, grotesque relationship:
He had the eye of a vulture....Whenever it fell upon me my blood ran cold; and so by degrees, very gradually, [as he becomes more obsessed] I made up my mind to take the life of the old man, and thus rid myself of the eye forever.
The ghastly thing is that they were on very familiar terms, if not friends. As they were both living in the same house, one could imagine that they were both tenents (each renting out a room) or that one of them was the owner and landlord. The narrator points out that he had shown himself to be very friendly towards the old man and that he had no personal grievance against him or motive to kill him other than to get rid of the vulture-like eye. This strikes out the possibility of revenge or greed. The lack of a murder motive affirms the psychopathic nature of the narrator, even his insanity.