murder will out
纸包不住火
A:In my opinion, someone else has caused the fire of this house.
A:我想，有人故意纵火烧了这所房子。
B:Who do you think that has the motive?
B：你觉得谁有这样的动机呢?
A:I'm not sure now. In any case, let's first make some careful investigations.
A:现在我还不能确定，无论如何，我们慢慢调查。
B:OK, murder will out!
B：好的，事情总会水落石出的，纸包不住火。
A:Yeah.
A：就是。