The trial commences the following morning. Victor is extremely apprehensive as to what the verdict will be: he is tortured by the thought that his "curiosity and lawless devices" will cause not one death, but two. He mournfully reflects that Justine is a girl of exceptional qualities, destined to lead an admirable life; because of him, her life will be cruelly foreshortened. Victor briefly considers confessing to the crime, but realizes that, as he was at Ingolstadt on the night of the murder, his confession would be dismissed as the ravings of a madman.
In court, Justine stands calmly before her accusers; her solemn face lends her an exquisite beauty. The prosecutor brings forth a number of witnesses, who provide compelling evidence against her: she was out for the whole night on which the murder was committed; she was seen near to the spot where the body was found; when questioned, she gave a confused and unintelligible answer; and she became hysterical at the sight of William's body. The most damning piece of evidence, however, is the fact that William's miniature, which he had been wearing at the time of the murder, was found in the pocket of Justine's dress.
Justine, called to the witness stand, provides another account of the events: with Elizabeth's permission, she had passed the night of the murder at her aunt's house in Chêne. Upon hearing of William's disappearance, she spent several hours searching for him; unable to return home, as it had grown too late, she determined to spend the night in a nearby barn. Justine says that if she was near the body, she did not know it; her confusion was only a manifestation of her tiredness. She remains unable to explain how the picture came to be on her person; she can only assume that the murderer himself placed it there.
Though few witnesses are willing to come forth to aver Justine's innocence, Elizabeth insists on speaking on the girl's behalf. She praises Justine's character, and says that she was beloved by the entire Frankenstein family; Elizabeth, for he part, will never believe that Justine is guilty. Despite this brave display of loyalty, Justine is condemned to death. Victor considers Justine's plight to be less than his own she is consoled by the fact of her own blamelessness, while he must live with his guilt.
Shockingly, Justine confesses to the murder, and expresses a wish to see Elizabeth, who asks Victor to accompany her. Justine tells them that she confessed to a lie in order to obtain absolution and avoid excommunication in her last moments. She does not fear death, and nobly spends her last moments in comforting Elizabeth and Victor. This only serves to heighten Victor's anguish, and he reflects that Justine and William are the first victims of his "unhallowed arts."