Since the early 1960's, the Sheriff's Office realized a need for specialized investigators who had the training and aptitude for the detailed forensic aspects of investigation. The duties of the investigators at that time were primarily centered on locating, developing, comparison and the identification of fingerprints found at scenes and the identification of deceased individuals by fingerprints. The investigators were also responsible for photography at major crime scenes. Due to the detail-oriented skills they possessed, they also became the technical experts for the collection of trace evidence and scene documentation as well.

Over time technological advances have been made and as a result the role of these investigators has grown. The Crime Scene Investigation Unit Detectives are now trained on advanced techniques for latent fingerprint development and other forensic aspects of scene investigation. The CSI Unit also performs additional skills such as bloodstain analysis, serial number restoration, indented writing development, electrostatic dust print lifting, digital image enhancement, computer and cellphone forensics, three dimensional laser mapping, DNA collection and examinations for trace evidence utilizing state-of- the-art forensic laser techniques.

Due to the technical nature of certain crimes, the CSI Unit works collectively with the Silicon Valley Internet Crimes Against Children Task Force and the National Center for Missing & Exploited Children to investigate internet crimes against children in the Sonoma County Sheriff’s jurisdiction and contract cities.

In 1996, the Unit was assigned the collateral duty of Environmental Crimes Investigation. This decision was based on the Unit's pre-existing knowledge and experience of working with and around hazardous chemicals within the CSI Unit's laboratory.