What is/are the motif(s) of the story?

One motif in any Poe story that involves murder is that the victim is often murdered in an animalistic, completely inhuman way. Even the old man and the way he looks is compared to an animal - a human with a "vulture eye" - a horrible eye which was covered with a pale, blue film. The vulture is a scavenger and the narrator tries to convince us that he is a victim of that scavenger; thus, he must kill and dismember the old man.