"The Zodiac Killer or Zodiac was a serial killer who operated in Northern California from at least the late 1960s to the early 1970s. The killer's identity remains unknown. The Zodiac murdered victims in Benicia, Vallejo, Lake Berryessa, and San Francisco between December 1968 and October 1969. Four men and three women between the ages of 16 and 29 were targeted. The killer originated the name "Zodiac" in a series of taunting letters sent to the local Bay Area press. These letters included four cryptograms (or ciphers). Of the four cryptograms sent, only one has been definitively solved."
The link below is you a website that has case files, suspects/persons of interest, ciphers, and all kinds of information about the Zodiac.
The movie, based on the actual killings, do a pretty good job portraying what actually happened.