The decision to make the murderer an animal makes it more palatable to society in 1841 when culture did not take as kindly to random violence (as in this story) compared to violence driven by emotion (i.e. Shakespeare’s works). Also it was a clever plot twist as most people reading a mystery assume that one of the human characters in the story is responsible and they try to solve the mystery accordingly. They are more likely to be surprised by the actual ending. In this way Poe was able to publish a brutal murder mystery and attribute it to the acts of an animal that knows no better rather than a human being so terrible. A well played publishing machination.