According to former FBI profiler John Douglas, many serial killers are motivated by a "desire to create and sustain their own mythology."  One of the most complicated cases along those lines, in which the geography of a series of murders seemed to play a part, was that of the Zodiac killer.  He operated in and around San Francisco, California, in the late sixties.

Exactly which murders are to be credited to him is controversial, in part due to inconsistencies in his own letters to the police and the press.  Only after someone made a connection to the 1966 killing of Cheri Jo Bates in Riverside, for example, did "Zodiac" claim that it was his.  Yet the vicious crime did seem to bear his signature, and letters were sent to the police, the press, and to Bates's father in a way that echoed the Zodiac's later communiqués. 

The next incident was the murder of a couple, David Faraday and Betty Lou Jenson, on December 20, 1968.  It took place near the town of Vallejo, north of San Francisco.  In the same general area, in July, 1969, another couple, Darlene Ferrin and Michael Mageau, were assaulted with a semiautomatic gun, and only Michael survived.  He managed to provide a description, but no one was arrested. 

Then letters arrived at the San Francisco Chronicle, San Francisco Examiner, and the Vallajo Times-Herald, each containing specific references to the murders along with what turned out to be one-third of a code.  The three pieces had to be published and put together to give someone a chance to crack it.  There were many attempts and finally a letter emerged, from the symbols, that was written by a man skilled at ciphers that attested to how much he loved to kill—especially people.  A week later another letter came to the Vallejo paper specifically from "the Zodiac."

All leads went nowhere until there was another attempted double murder at Lake Berryessa of a couple (killing the girl), and the near-public slaughter in the city of a cab driver.  These deaths were followed by a letter that contained a piece of the driver's bloody shirt, which alerted police to the possibility of an arrogant madman in their midst—especially when he sent another letter that warned of a bomb.  The communications kept coming and even though there was nothing more than the abduction of a woman who escaped, Zodiac kept taunting police until 1984.  He claimed a mounting number of deaths---although none were verified---of as many as 37 people.

What gave the Zodiac case a decidedly geographical edge was the result of a map that he himself sent of Mount Diablo, a bay area landmark.  Something interesting would be found, he said, if the police placed a "radian" on Mount Diablo.  A radian is a unit of angular measure used by engineers and mathematicians of 57 degrees, 17 minutes, 44 seconds.  It is an angle over an arc whose length is equal to the radius of a circle, of which the arc is part.  If a radian is placed on the map with the apex on Mount Diablo and one leg of the angle across the Vallejo murder sites, then the other goes through Presidio Heights in San Francisco, where the cabbie was killed.  According to the school of thought that believes this to be a valuable clue, the victims appear to have been chosen not because of who they were but to mark a particular time and place.

This clue shifted the investigation somewhat, because it appeared to be the case that the suspect was more likely to be a man with a higher IQ than had first seemed evident from the illiterate tone of the letters.  The misspelled words and poor grammar now appeared to be more a clever manipulation than a genuine expression of the killer's limited abilities.