There is significant circumstantial evidence to suggest that the man who terrorized the San Francisco Bay Area under the persona of the Zodiac began his life as a killer several years earlier on a beach in Santa Barbara County. There, in 1963, an as-of-yet unidentified person brutally murdered Robert Domingos and Linda Edwards, two Lompoc, California high-school seniors who were unofficially participating in an annual rite of passage: senior ditch day.
John B. Averitt, Ph.D., a high-school friend of Robert and Linda at the time of their deaths, has created an excellent five-part series on YouTube that details the circumstances surrounding the murders and the subsequent investigation. As someone who has been to the crime scene and spent time finding and reading numerous newspaper articles published on the subject of the murders, I appreciate the detailed insights that Dr. Averitt is able to provide. I recommend you check it out.