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Indisputably incriminating evidence. Likened to a gun that is still smoking after having been fired. A smoking gun was revealed in the form of emails documenting the man's involvement in the money laundering scheme. So far the prosecutor has presented only circumstantial evidence, but she's expected to reveal a smoking gun against the defendant soon.
Something that serves as indisputable evidence or proof, especially of a crime. For example, There is no smoking gun in the Oval Office; the President had no role in tampering with the evidence . This expression alludes to the smoke coming from a recently discharged firearm, a normal occurrence until the invention of smokeless powder. [Mid-1900s]
a smoking gun
COMMON If you talk about a smoking gun, you mean a piece of evidence which proves that a particular person is definitely responsible for a crime. The search for other kinds of evidence failed to produce a smoking gun. First of all, there's no smoking gun. In the course of our investigation we did not find a single piece of evidence.
n. the indisputable sign of guilt. The chief of staff decided that the admiral should be found with the smoking gun.