Can you go deeper into the psychology and actions of Casanova?

Casanova started killing beautiful women as a teenager. Even then, he chose the most desirable and unattainable women he could find. He had them and then killed them. Casanova is different. Like his namesake, he is a lover. He is not burdened with the emotional scars that affect Rudolph. Casanova leads a double life with his loving wife. He is not incapable of love like Rudolph. Perhaps the opposite is true: he loves women too much. He is always searching for the perfect woman. Casanova relishes power. The girls must follow his rules or they will be killed. He is a very strong man. Kate is shocked by his strength and thinks of him as an animal, he is so powerful. He neutralizes Kate's power with his strength, his stun gun and his drugs.

It is unlikely that Casanova ever would have been able to commit his crimes without joining forces and "twinning" with Rudolph. Rudolph, the brutal one, is an expert killer given to brutality. He brings that out in Casanova. Rudolph likely instructs Casanova on the use of drugs to subdue his victims. Remember, Kate thinks that Casanova is a doctor. In a sense he is, because of his link with Rudolph. Early in the novel, the "perfect crime" aspects of both cases make investigators think the killers are police. This is true as well. Casanova, the leader, shows Rudolph how to commit crimes without being caught. Once Rudolph is dead, Casanova is lost without him. He does not attack or kidnap any other women, and his attack on Cross and Kate fails miserably.

Twinning is a psychological theory that Cross applies to the case. Twinning is a phenomenon when two lonely people have an urge to bond. It is a fusion of two to form a single unit. In an unhealthy twinning, the pair joins for negative reasons. Cross' theory of Casanova and the Caller twinning progresses throughout the novel. They met in college when Casanova confronted the Caller about his murder of Roe Tierney. Casanova was likely conducting his surveillance of Ms. Tierney when he saw the Caller kill her. Casanova reached out to the Caller because they both shared a desire to take the women they wanted. They feed each other's sexual appetites. They compete with one another and are more powerful together. When they take on Cross and Sampson at the conclusion of the novel, they believe that if they work together, they can defeat them. By the end of the novel, Casanova is despondent because he has lost his twin. He has stopped kidnapping and is a shell of his former self.