How did the Zodiac Killer get his name?
This was a name that the killer chose for himself. No specific reason was ever given why but many have speculated on various reasons why he may have chosen this name. Because of the timing of his attacks and letters he apparently understood astrology.
The killer is thought to have modeled certain elements of his MO upon the villain of Charlie Chan at Treasure Island (1939). The villain of this film was named Zodiac, taunted the police and had many other similarities.
According to the bestseller Zodiac by Robert Graysmith the Zodiac may have based his name on a character in a book called The Most Dangerous Game. This book was published in 1924 and the villain of the story was named General Zaroff. A movie with the same name was made in 1932.
On August 1, the Vallejo Times-Chronicle, the San Francisco Examiner and the San Francisco Chronicle received near-identical letters from the Zodiac in which he took credit for the murders, proving his guilt by stating several facts about the crime scenes, such as what the victims were wearing, how their bodies were positioned and what brand of ammunition he used. The only signature was the Zodiac's symbol.