The Zodiac Killer was a notorious serial killer in California during the late 1960's to the early 1970's, who committed at least five known murders and possibly more, before he seemed to disappear.
The Zodiac Killer was infamous, not only for the murders he committed and his trademark symbol he left behind, but also for the ciphers, phone calls, and letters he sent to local police and news in the area, which was also how he gained publicity.
Once news got out about the Zodiac Killer, FBI and CIA have tried to decipher his messages, and many of them weren't solved, but one was solved by Donald Harden. He and his wife used common sense, patterns, and a reference book on coding. The letter that they decoded told about how Zodiac liked killing, and some other letters that have been decoded by others told about who he would kill.
The killer's alias, Zodiac, was most likely chosen by him because he may have had an interest in astrological symbols, which was indicated in the encryptions that were sent .
Zodiac's personality traits and even his past, factored into the reasons why he was killing, and indicated that he was intelligent and an introvert who had problems with his mother as a child, according to psychologists and criminal profilers on the Zodiac case.
Zodiac's MO ,(pattern of killing/certain people he killed), were young couples who were in isolated areas. He killed both men and women who were between 16-29. After a while, as government officials and police were unable to capture him, Zodiac started to change tactics and once threatened school children in a letter.
Betty Lou Jensen and David Faraday, who were high school student's during the time period of Zodiac's attacks, are closely associated with his murders. They were the first known victims of Zodiac's killings on December, 1968 on Lake Herman Road.
His last known victim, Paul Stine, was killed in a neighborhood street, which was a major change in Zodiac's MO. Stine was a taxi driver and was shot and killed on October 1969 in the Presidio Heights neighborhood in San Francisco.
Handwriting specialists have also found out some of his personality traits and parts of his past from his handwriting, like William F. Baker, a handwriting expert and psychologist.
“The strong slant to the left of the lower letters denotes a ‘mother hostility’ and an unhappy childhood. Carry that trait further and you find the man who is afraid of women and hates them. Carry that to a further extreme and you have a man who is capable of killing women to get even with his mother,” - William F. Baker