Sherlock Holmes phrase which originated in the book The Gloria Scott meaning indisputable evidence?

Answer:
Smoking gun.


Then we rushed on into the captain's cabin, but as we pushed open the door there was an explosion from within, and there he lay with his head on 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. -- Justice of the Peace Trevor, The 'Gloria Scott'
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