He therefore pretended to have arrested Marcello on the suspicion of an attempt to poison him.

Some large toads, bought by the young man at a high price two or three months earlier, lent color to this accusation.
Meanwhile the investigation was conducted as secretly as possible by the Duke in person, his brother-in-law Count Aliffe, and a certain Antonio Torando, with the sanction of the Podesta of Soriano.

After examining several witnesses, they became convinced of Violante's guilt.

Marcello was put to the torture, and eventually confessed.

The Duke stabbed him to death with his own hands, and afterwards cut Diana's throat for her share in the business.