In this two-part series, in Part One we break down the chilling beginnings of the Zodiac Killer case. We cover the known crimes, the victims whose lives were taken far too soon, and the letters that turned this case into a national obsession. From cryptic ciphers to taunting messages sent directly to the media, we walk through how one unidentified killer was able to spread fear across California and leave behind one of the most haunting mysteries in true crime history.