What mystery writer first coined the idiom ‘The Smoking Gun’?

In literature and legalese, ‘The Smoking Gun’ is an indisputably conclusive piece of evidence, stemming from the image of a person still holding a recently used firearm as proof of him being a murder or robbery’s perpetrator.

The most famous example of its legal use is a 1972 tape of a conversation in the Oval Office, which reveals President Nixon and his Chief of Staff discussing their plans to obstruct the Watergate burglary investigation.

However, the phrase is nearly 80 years older, first used in the ‘Adventure of the Gloria Scott', a short story written by Arthur Conan Doyle, in which Sherlock Holmes regales Dr. Watson with the tale of his first professional case. At its climax, Holmes’s client rushes into a room and sees the direct aftermath of a murder, with the guilty man literally holding a smoking gun.

The story first appeared in The Strand magazine in 1893, and was published with eleven other tales in “The Memoirs Of Sherlock Holmes”, a year later.