Possibly there was clear proof that he could have had no connection with the crime.
Now to examine more closely the actual motives given by those authorities and by later, critical writers, for attributing the guilt to Cesare.
In September of the year 1497, the Pope had dissolved the marriage of his daughter Lucrezia and Giovanni Sforza, and the grounds for the dissolution were that the husband was impotens et frigidus natura--admitted by himself.( 2) 2 "El S.de Pesaro ha scripto qua de sua mano non haverla mai cognosciuta et esser impotente, alias la sententia non se potea dare.

El prefato S.dice pero haver scripto cosi per obedire el Duca de Milano et Aschanio" (Collenuccio's letter from Rome to the Duke of Ferrara, Dec.
25, 1497).
If you know anything of the Italy of to-day, you will be able to conceive for yourself how the Italy of the fifteenth century must have held her sides and pealed her laughter at the contemptible spectacle of an unfortunate who afforded such reason to be bundled out of a nuptial bed.

The echo of that mighty burst of laughter must have rung from Calabria to the Alps, and well may it have filled the handsome weakling who was the object of its cruel ridicule with a talion fury.

The weapons he took up wherewith to defend himself were a little obvious.

He answered the odious reflections upon his virility by a wholesale charge of incest against the Borgia family; he screamed that what had been said of him was a lie invented by the Borgias to serve their own unutterable ends.( 1) Such was the accusation with which the squirming Lord of Pesaro retaliated, and, however obvious, yet it was not an accusation that the world of his day would lightly cast aside, for all that the perspicacious may have rated it at its proper value.
1 "Et mancho se e curato de fare prova de qua con Done per poterne chiarire el Rev.Legato che era qua, sebbene sua Excellentia tastandolo sopra cio gli ne abbia facto offerta." And further: "Anzi haverla conosciuta infinite volte, ma chel Papa non geiha tolta per altro se non per usare con lei" (Costabili's letter from Milan to the Duke of Ferrara, June 23, 1497).
What is of great importance to students of the history of the Borgias is that this was the first occasion on which the accusation of incest was raised.