Why are murder mysteries written in first person?

Murder mystery fans like to figure out whodunit. It’s why the genre is fun, and enthusiasts hate it when the author rigs the game. No undisclosed facts or coincidences can miraculously solve the crime. Everything known to the detective must also be known to the reader. The most effective way to share information is to tell the entire story in first person. First person requires the narrator to be present in every scene, so everything she sees, the reader sees. Thus, most murder mysteries are written in first person in order to insure a fair challenge.

All the facts must be commonly known, but it’s legitimate to shield the reader from the thoughts of the detective. This is why many authors don’t use the protagonist’s point of view. The first person character can be a narrator sidekick, like in the Sherlock Holmes mysteries which are told by Dr. Watson. This is a handy device for facilitating a surprise ending. Although readers get to know all the facts, they don’t see the detective mentally unravel the incongruities of the mystery.

When I was figuring out a plot for the third Steve Dancy Tale, it occurred to me that I had all the elements in place for a murder mystery. I had started the series in the first person and another main character worked for the Pinkerton National Detective Agency. Everything fit for a murder mystery disguised as a western. Murder at Thumb Butte is a murder mystery that just happens to occur in the Arizona Territory. Since there were plenty of murders in the Old West, why couldn’t a mystery surround the one Steve Dancy needed to solve to save a friend? 

Honest Westerns ... filled with dishonest characters