The evidence is irrefutable. The headlines declare a "smoking gun" has been found. But how did this dramatic image of a phrase become synonymous in everyday speech with conclusive proof? Fittingly, the origins lie with one of the world's most famous fictional detectives, and of course, a recently fired pistol.

The 1893 Arthur Conan Doyle short story "The Adventure of the 'Gloria Scott'" depicts a young Sherlock Holmes solving his first professional case. Holmes was asked by a college friend to decipher a mysterious letter that had caused his father to drop dead. It turned out to be blackmail related to a mutiny that the father had organized on a prison ship taking him to Australia long ago. In the story's climactic flashback to the event, the father explains the mutineers were forced to quickly massacre the crew when their stash of guns was discovered by the ship's doctor. After shooting several guards, they moved to seize control of the ship:

"[W]e rushed on into the captain's cabin, but as we pushed open the door there was an explosion from within, and there he lay wit' his brains smeared over the chart of the Atlantic which was pinned upon the table, while the chaplain stood with a smoking pistol in his hand at his elbow."

"A good copy editor would have fixed Doyle's awkward 'in his hand at his elbow,' and Sir Arthur chose pistol rather than gun," wrote the late William Safire in his "On Language" column for the New York Times Magazine in 2003. Nevertheless, those quibbles aside, he identifies Doyle's use of the phrase as "the start of the cliché that grips us today."

But 'smoking gun' wouldn't reach cliché status until some 80 years after the short story was published, Safire notes. That's when the Watergate crisis lodged it firmly into the American lexicon. A New York Times article written during the height of the scandal on July 14, 1974, notes the main question members of Congress were asking as they considered impeaching President Richard Nixon was "Where's the smoking gun?"

When the president released the recording of a conversation between him and Chief of Staff H.R. Haldeman that August, revealing he had ordered a cover-up of the Watergate Hotel burglary, the damning evidence was quickly dubbed the "smoking-gun tape."

In the 40 years since then, the phrase has found use in investigations of world politics, the tech industry and even reality television. For political columnist Jonah Goldberg, the phrase has become so enduring that it's created an unrealistic standard of the proof required for a scandal.

Cliché or not, it's clear that for writers everywhere, when it comes to surefire evidence, guns will keep on smoking.