A murder mystery requires a unsolved crime. An investigator (protagonist) has to unravel the mystery by putting the clues and evidence together to catch the criminal. There are two ways this can be approached. The two story types are Open and Closed. This can be better explained by looking at murder mystery films and TV shows.
At the beginning of the film, the audience are shown the perpetrator committing the ‘perfect crime’. We know who did it and how. The question is will they get caught? The show follows the protagonist as they attempt to unravel the story and unmask the guilty party.
The classic ‘whodunit’. Neither the audience nor the protagonist know the identity of the murderer. In this case the story concerns finding out what happened, but also know is involved. There is a different element of suspense involved when the audience know as much, or as little, as the investigator.
Columbo was an American television series which used the Open format. The shows began by showing the crime and its perpetrator. The story unfolded to show how the perpetrator was finally be caught and exposed. The show’s writers called this method of murder mystery a “howcatchem,” rather than a “whodunit”.