English version

smoking gun

From Longman Dictionary of Contemporary Englishsmoking gunˌsmoking ˈgun noun [countable]  something that shows who is responsible for something bad or how something really happened
Examples from the Corpus
smoking gunInvestigators have failed to find a smoking gun to connect the mayor to the missing money.The Internal Revenue Service thought it had a smoking gun.Federal agents and prosecutors said they found what amounts to a smoking gun in the case.
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