When Edgar Allen Poe published Murders in the Rue Morgue in 1841 the murder mystery was a relatively new genre. He wrote a few more of these increasingly popular detective stories. However, In 1849 he was found wandering injured and delirious through the streets of Baltimore. The brilliant writer never regained a clear enough mind to explain what had happened to him. He died a few days later leaving a real unsolved mystery. 

Poe’s fictional detective, C. Auguste Dupin, gained some attention, too. Another author even took a few pot shots at him in his own first murder mystery entitled A Study in Scarlet. Anyone familiar the murder mystery genre will recognize that novel as the one introducing Sherlock Holmes and Dr. Watson to the world in 1887. Arthur Conan Doyle, a medical doctor and aspiring author, used a real inspiration for Sherlock Holmes. His consulting detective had such a striking resemblance to a surgical instructor at the University of Edinburgh Medical School that many of Doyle’s contemporaries realized he modeled Holmes after Joseph Bell. 

These two authors of mysteries introduced some of the staples of this genre. The calling card, the modus operandi (or M.O.), and the motive. The calling card is also called the signature aspect in criminology. It is a quirky behavior or an eccentric ritual that seems to exhibit pure hubris. It is often the item that marks crimes committed by the same perpetrator. In A Study in Scarlet, the word “rache” (German for revenge) is written in blood near the victim.

Modus operandi is Latin for method of operation describing the character’s preferred way of interacting with others to carry out their crimes. Non-criminals also have M.O.s. Consider two different teenage boys in their attempts to attract a certain teenage girl. One may decide a show of physical strength, such as pelting a rival with a football, to gain attention from the female. The other, who uses his wit may point out the disproportionate number of felons in the NFL after the pelting incident. 

Motive is the reason that drives a criminal (or any character) to act. Simply being crazy is not a real motive, but the character must be seeking a specific reward from the crime. The rationale for committing crimes tends to remain constant while the M.O. is not completely fixed but can change over time. Often criminals gain confidence and becomes more daring. However, there still needs to be a reason, or an event that causes the shift in the M.O. 

Calling card, modus operandi, and motive are not just reserved for suspects in murder mysteries.  Fictional characters take on their own personalities when you remember to consider each of these features. These aspects don’t make characters completely predictable, otherwise criminals would be easier to catch, but they do make characters more memorable.