One of the major themes in I’ll Be Gone in the Dark is how a criminal like the Golden State Killer evolves from a burglar into a serial killer. Though the GSK’s identity is unknown, he leaves behind numerous pieces of evidence that offers McNamara insight into his crimes. The portrait McNamara creates is one of a criminal tormented by violent sexual fantasies. Each time the GSK commits a crime, he needs to increase the level of brutality in order to achieve the same states of euphoria and pleasure. 

McNamara suggests that the GSK begins his crime spree as a burglar, known as the Ransacker (though the link between the two criminals is not conclusive). As the Ransacker, the GSK breaks in to numerous homes throughout Visalia. Instead of stealing items, however, the GSK trashes the house, often arranging woman’s underwear throughout the home. In these crimes, the GSK seems motivated by a desire to violate homeowners’ sense of security and safety. Six months after his crime spree in Visalia, the GSK begins committing crimes in Sacramento. Breaking into peoples’ homes is no longer enough to provide the GSK with his desired thrills. Instead, the GSK begins to rape women, first targeting single women before moving onto couples.