Cicero, Pro Milone 32
“How, then, is it possible to prove that Clodius conspired against Milo? For such an audacious, nefarious monster it is enough to show that he had a great reason, that great hope resided in the death of Milo, and that there was great purpose to it. And so, let that proverb of Cassius “Who profited from it?” [cui bono fuerit] frame the players on the stage, if truly good men are compelled to deception by no prize while the wicked often are moved by a small one.
Once Milo was killed, Clodius advanced in these ways: not only was he as a praeter under no consul who would do something about his crime, but he was also a praeter serving under consuls with whose plans if not their actually help he hoped that he would be able to get away with his planned insanities. These men, as I am sure we were thinking, would not want to restrain his actions if they could, since they would think about the great benefit they owed him; men who, even if they wanted to, would hardly be capable of squashing the boldness of the most criminal person, an audacity fully strengthened by time.”
Quonam igitur pacto probari potest insidias Miloni fecisse Clodium? Satis est in illa quidem tam audaci, tam nefaria belua docere, magnam ei causam, magnam spem in Milonis morte propositam, magnas utilitates fuisse. Itaque illud Cassianum, “cui bono fuerit,” in his personis valeat, etsi boni nullo emolumento impelluntur in fraudem, improbi saepe parvo. Atqui Milone interfecto Clodius haec adsequebatur, non modo ut praetor esset non eo consule, quo sceleris nihil facere posset, sed etiam ut eis consulibus praetor esset, quibus si non adiuvantibus, at coniventibus certe speraret posse se eludere in illis suis cogitatis furoribus: cuius illi conatus, ut ipse ratiocinabatur, nec cuperent reprimere, si possent, cum tantum beneficium ei se debere arbitrarentur, et, si vellent, fortasse vix possent frangere hominis sceleratissimi conroboratam iam vetustate audaciam.
The Cassius in question is L. Cassius Longinus, Tribune of the Plebs in 127 BCE . We have mentioned the polarizing P. Clodius Pulcher before.
Cicero was a fan of this saying.
Cicero, Pro Sexto Roscio Amerino, 84
The famous Lucius Cassius, whom the Roman people used to consider the most truthful and wisest judge, often used to say in evaluating cases “who stood to profit” [cui bono fuisset]. This is the human way: no one pursues a crime without the hope of some profit.”
Cassius ille, quem populus Romanus verissimum et sapientissimum iudicem putabat, identidem in causis quaerere solebat, “cui bono” fuisset. Sic vita hominum est, ut ad maleficium nemo conetur sine spe atque emolumento accedere.