The real-life Zodiac killer, who terrorized the California Bay Area in the late 1960s, was never caught. That fact in itself renders the potential for a most compelling story. But if you're going to make a movie about this case, who or what does your movie focus on? You can't focus on the killer himself because you don't know who he is. This might seem like a problem for movie makers. But for a clever film producer the killer's anonymity presents an opportunity.
"The Zodiac" (2005) focuses on a fictional lead detective, a man named Matt Parish (Justin Chambers), his wife and his young, never smiling, son who fixates on his dad's detective work. The plot thus gets sidetracked onto this fictional family, their home life, and how this unsolvable case affects each of them. And we have lots of filler scenes with archival footage of the era, including the moon landing, Vietnam, Nixon, but precious little about the Zodiac. The film thus comes across as tedious, trite, and largely irrelevant, lacking suspense and tension.
Visually the film trends dark with a moody tone, both appropriate for the topic. Casting and acting are acceptable except for the annoying and unnecessary William Mapother. Cinematography and production design are competent. But the music is overly dramatic.
My impression is that the film's producers wanted to capitalize on this famous case with the word "Zodiac" in the title. The film could then show how the phantom killer, never seen, always in the background and obscured, could affect the lives of ordinary people in the community. The result is a mostly generic, opportunistic script that could be applied to almost any unsolved serial killer case.