Cui bono

Cui bono ("Good for whom?", "For whose advantage?", or "Who benefits?") is a Latin adage which means that the person or people guilty of committing a crime may be found amongst those who have something to gain, perhaps financially.

Although the principle is useful in criminal investigations, the party with the most to gain may not always be obvious, or the guilty party may distract attention by diverting attention on to a scapegoat.

The expression is said to have been coined by Roman consul and censor Lucius Cassius Longinus Ravilla, and was used by Marcus Tullius Cicero.