Cui bono

Cui bono (/kwiː ˈboʊnoʊ/), literally "to whose profit?", is a Latin phrase which is still in use as a key forensic question in legal and police investigation: finding out who has a motive for a crime. It is an adage that is used either to suggest a hidden motive or to indicate that the party responsible for something may not be who it appears at first to be.