Cicero, Pro Roscio (85-86):
That Lucius Cassius whom the Roman people thought the most honest and wisest judge used to ask over and over again in his cases, ‘To whom was this beneficial?’ Human life is so constituted that no one would attempt to approach any evil deed without some hope and some emolument. Those, to whom some danger was created because although he was a friend of truth, he was not by nature so much inclined to pity as given to severity, used to fear and flee from this inquisitor and judge.
For my part, although a man most boldly ranged against audacity and most merciful to the innocent is set at the head of the case, yet I would willingly suffer myself to speak for Sextus Roscius even with that most penetrating judge Cassius presiding, or even among the Cassian judges, whose name even those who must speak the case now still fear. When they see in this case that those men possessed the most ample fortunes while this man was stuck in the depth of poverty will not ask to whom was this beneficial?, but with that being clear enough already they will join the crime and the suspicion rather to the receipt of a reward than to the inheritance of poverty. What if it had happened had you previously been a slight person? What if you had been greedy, or audacious, or the greatest enemy to the man who was killed? Would we then need to ask what reason drew you on to such a crime? What part of this can be denied? The insignificance of such a person is such that it cannot be disguised, and it shines forth more obviously the more he attempts to hide it.
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. Hunc quaesitorem ac iudicem fugiebant atque horrebant ei quibus periculum creabatur ideo quod, tametsi veritatis erat amicus, tamen natura non tam propensus ad misericordiam quam applicatus ad severitatem videbatur. Ego, quamquam praeest huic quaestioni vir et contra audaciam fortissimus et ab innocentia clementissimus, tamen facile me paterer vel illo ipso acerrimo iudice quaerente vel apud Cassianos iudices, quorum etiam nunc ei quibus causa dicenda est nomen ipsum reformidant, pro Sex. Roscio dicere. In hac enim causa cum viderent illos amplissimam pecuniam possidere, hunc in summa mendicitate esse, illud quidem non quaererent, cui bono fuisset, sed eo perspicuo crimen et suspicionem potius ad praedam adiungerent quam ad egestatem. Quid si accedit eodem ut tenuis antea fueris? quid si ut avarus? quid si ut audax? quid si ut illius qui occisus est inimicissimus? num quaerenda <causa> quae te ad tantum facinus adduxerit? Quid ergo horum negari potest? Tenuitas hominis eius modi est ut dissimulari non queat atque eo magis eluceat quo magis occultatur.