"Thus spoke my prophetic soul, as torn by remorse, horror, and despair, I beheld those I loved spend vain sorrow upon the graves of William and Justine, the first hapless victims to my unhallowed arts." (page 60)
After Justine takes the blame for little William's death, she pledges her innocence to Elizabeth and Victor. This realization that Justice is going to be killed for a crime she didn't commit sends Victor over the edge. His feelings of guilt grow to almost an intolerable level, and he becomes even more resentful towards the monster he created. Seeing it as responsible for the death of two people he loved, these circumstances further Victor's hatred for the creature and make him realize he has to find a way to ensure its good riddance. This also gives Victor another element of power in the story since only he holds the knowledge that can save Justice. He is the only one who knows of the existence of the monster and is convinced of its guilt, but he is hesitant because he doesn't think that anyone will believe his story. Ironically, the character who is condemned to death for an act she didn't make is named "Justice". I don't think that's true justice at all, and I think that most people would agree with me.