The people most noted - for obvious reasons - for using the words: "I rest my case" are lawyers. Usually, they have been presenting evidence on behalf of a client in an effort to excuse him/her of any guilt for the crime being considered. Clearly, then, when the lawyer stopsmaking the excuses he hopes will exonerate the person in the dock, he has reached the point at which it makes sense to say: "I rest my case." QED