"Cui bono?" is a phrase you'll often see used on conspiracy-minded Youtube videos and discussion forums. It's Latin for "Who benefits?", and it refers to a perspective in legal analysis that the one who stands most to gain from a crime is often the perpetrator. It's the "motive" part of "means, motive and opportunity".
The term comes up in conspiracy circles a lot because motive is often the biggest plot hole in the official story promoted by the authorized narrative managers of the political/media class about a given event.