smoking gun

1. N-COUNT A smoking gun is a piece of evidence that proves that something is true or that someone is responsible for a crime. 确凿的证据; 确证证据[美国英语] [usu sing]

The search for other kinds of evidence tying him to trafficking has not produced a smoking gun. 在其它方面还没有找到能证明他参与此非法交易的确凿证据。