 In a letter to friend Dr. Joseph Snodgrass , Poe said of " The Murders in the Rue Morgue " , " its theme was the exercise of ingenuity in detecting a murderer . " Dupin is not a professional detective ; he decides to investigate the murders in the Rue Morgue for his personal amusement . He also has a desire for truth and to prove a falsely accused man innocent . His interests are not financial and he even declines a monetary reward from the owner of the orangutan . The revelation of the actual murderer removes the crime , as neither the orangutan nor its owner can be held responsible . Later detective stories would have set up M. Le Bon , the suspect who is arrested , as appearing guilty as a red herring , though Poe chose not to . 
