At the age of 26, that great Roman patron, politician, and self-promoter, Marcus Tullius Cicero, made a name for himself defending Sextus Roscius against a charge of parricide. Cicero said this;
L. Cassius ille quem populus Romanus verissimum et sapientissimum iudicem putabat identidem in causis quaerere solebat "cui bono" fuisset.
The famous Lucius Cassius, whom the Roman people used to regard as a very honest and wise judge, was in the habit of asking, time and again, "To whose benefit?"
He then went on to argue that as it was the prosecution themselves who had benefitted from the death of Sextus’ father, that they were the more likely murderers. QED.
cui bono? is arguably the most famous example of Latin’s Double Dative construction, so called because both cui and bono (a Pronoun and Noun respectively) are in what is called the Dative Case.
The first Dative (cui) refers to the person or thing concerned. The second (bono) to the role something serves. Here are some examples. canis est auxilio colono. The dog is a help to the farmer. Both auxilio help and colono farmer are Dative. haec sententia est exemplo discipulae. This sentence is an example for the student. Both exemplo example and disciplae student are Dative. cui bono? cui To whom [was it] bono a benefit?
On today’s page, Marcellus receives $100 from the sale of his painting. pecunia maximo adlevamento est Marcello. The money is a huge relief to Marcellus. Both maximo adlevamento huge relief and Marcello are Dative.
The money is a huge relief to Marcellus. He places it immediately in an envelope (involucro). Tomorrow he will carry the envelope to the bank.