smoking gun
term used in reference to an object or fact that serves as conclusive evidence of a crime or similar act, just short of being caught in flagrante delicto
en-GB/ˈsməʊkɪŋ ˈɡʌn/
en-US/smɑˈkiŋ ˈɡʌn/
term used in reference to an object or fact that serves as conclusive evidence of a crime or similar act, just short of being caught in flagrante delicto