Lucretia herself stated she was willing to swear to this.
During these proceedings her spouse was in Pesaro.

Thence he subsequently went in disguise to Milan to ask the protection of Duke Ludovico and to get him to use his influence to have his wife, who had been taken away, restored to him.

This was in June.

He protested against the decision which had been pronounced in Rome, and which had been purchased, and Ludovico il Moro made the naive suggestion that he subject himself to a test of his capacity in the presence of trustworthy witnesses, and of the papal legate in Milan, which, however, Sforza declined to do.[55] Ludovico and his brother Ascanio finally induced their kinsman to yield, and Sforza, intimidated, declared in writing that he had never consummated his marriage with Lucretia.[56] The formal divorce, therefore, took place December 20, 1497, and Sforza surrendered his wife's dowry of thirty-one thousand ducats.
Although we may assume that Alexander compelled his daughter to consent to this separation, it does not render our opinion of Lucretia's part in the scandalous proceedings any less severe; she shows herself to have had as little will as she had character, and she also perjured herself.
Her punishment was not long delayed, for the divorce proceedings made her notorious and started terrible rumors regarding her private life.
These reports began to circulate at the time of the murder of Gandia and of her divorce from Sforza; the cause of both these events was stated to have been an unmentionable crime.

According to a reliable witness of the day it was the lord of Pesaro himself, injured and exasperated, who first--and to the Duke of Milan--had openly uttered the suspicion which was being whispered about Rome.