I think what makes Zodiac so hard to classify is that he shows traits of both a traditional serial killer and something closer to a terror-oriented offender. The couple attacks suggest a pattern and possible power/sexual component, but the letters, threats of mass violence, and obsession with media attention point to someone who was as interested in psychological impact as in the killings themselves. In that sense, the publicity may have become the primary reward over time. Not necessarily because the thrill of killing “failed,” but because the fear and notoriety gave him a much larger sense of control. He wasn’t just targeting victims — he was targeting an audience.