Profile of the Zodiac Killer
The killer constantly changed his method of operating and openly admitted that murder was sport for him. The attacks occurred at dusk or after dark, on weekends, often around holidays, with different weapons and apparently with no motive save violence itself. Clearly, the killer wanted credit for them and he turned most of his rage against females.
Possible motives were to prove his superiority, get attention, control the investigation, create a terroristic climate, and relive the crimes via media reports. Going after couples, which he did three times, could indicate that he was envious or jealous because he did not (or could not) have that kind of relationship. It might also have been to show that he was not afraid to confront a male, although the fact that he targeted three couples when he could have only shot lone females or lone males indicates resentment about relationships.
He liked to ambush his victims, yet for him none of these incidents were high risk crimes. While they were out in the open, they were not risky. Even when he set himself up for a potential risk, by being interviewed by phone, for example, he usually withdrew. Yet it's possible that he believed he was taking a risk, so he could congratulate himself when he did not get caught. Maybe he viewed these crimes as proof of his skill in stealth. He might have fantasized about himself being more daring than he actually was. By all witness accounts, he appeared to be late twenties to early thirties, heavyset, strong, and aggressive. It wouldn't be surprising that his fantasies of being a skilled "hunter" grew from an immature and insecure mind.
Nevertheless, the man who called himself the Zodiac was organized, intelligent and meticulous. If we take the reference to the Zodiac seriously, we find several symbols in his initial cryptogram that look like the symbol for Taurus the bull, which could identify his approximate birth date. He obviously liked astrology and might have viewed himself as fated by the stars. Those close to him would probably have heard him engage in knowledgeable discussions about astrological symbols and meanings.
Among the most engaging aspects of the crimes for him was to be able to taunt the authorities from a superior perspective and to watch the police make fools of themselves. This often indicates a person who feels uncertain about his intelligence, so to reassure himself, he plays games with others. The Zodiac needed to think he was smarter than even the best detectives, and he probably exaggerated the risks he took in order to affirm his smug sense of superiority. People who knew him would have been familiar with his arrogance, as well as his shortcomings and insecurity.
He used a lot of diversionary tactics, such as making threats that turned out not to be true, or posing cryptic mysteries. This is a form of what's called "duping delight." He's excited by duping others. The puzzles he presented probably meant nothing, but this man enjoyed knowing that a whole city full of people, as well as a number of law enforcement agencies, were at work on whatever code or clue he sent. That would have given him a thrill, knowing that the resolutions were merely dead-ends, and yet people would keep trying to find out what they meant. The closer they thought they were to identifying him, the more it would have amused him.
He enjoyed the control he exerted because he was in charge; he was running the investigation, more or less, as though he was the supervisor. He might have had pretensions of being a police officer, but for some reason been barred from this profession. This way, with these threats, he got to order them about. When he moved from the Vallejo area into San Francisco for his murders, he acquired a greater venue for control, along with the ability to spread the terror and feel more powerful. For him, it was all about that. He exerted control over his victims, and he did the same with anyone who was concerned about becoming a random victim.
He especially enjoyed controlling the newspapers and the police agencies of a town the size of San Francisco. He liked knowing they got into tiffs over territory and investigative squabbles. To his mind, that was more evidence of how stupid they were, and each day that went by without them catching him reinforced this opinion and sense of superiority. Every communication he sent fueled that fire.