Note: I walked into Zodiac knowing very little about the real Zodiac case, which is the best way to see the movie. If you plan on seeing it, you should try to go in as blind as possible.
Like an American Jack the Ripper, the Zodiac serial killings were so notorious and mysterious that they stayed in the public consciousness long after other equally evil murderers were forgotten. The reason, I think, was because of the killers need for public attention- insisting that his cryptic letters be published in newspapers, along with codes revealing- more ambiguous messages. If you take away the fact that real people were murdered, it is almost like one of those city-wide scavenger hunts that companies put on to raise publicity.
David Fincher's film about the killings is a crime procedural in the best sense- there is an air of realism and plausibility that is often lacking in movies like Dirty Harry, which the characters at one point see. The policemen are played by Mark Ruffalo and Anthony Edwards, and they are aided by Robert Graysmith (Jake Gyllenthall), a cartoonist at the San Francisco Chronicle who takes up an interest and latter obsession with catching the real Zodiac, and it's easy to see why- it answer always seems to be one step away from the investigators, but every new clue just uncovers more and more questions.
Throughout the years, people on the case, both in the police force and on the newspaper, get fired, quit, and generally have life happen to them. Unlike most thrillers, there is no dramatic irony- the audience does not know who the killer is- so we follow the characters as each lead unfolds.
Fincher is one of the best directors working in Hollywood. This film continues the dark tone of the director's other films (I have seen them all except The Panic Room) but has a less impressionistic style. Fincher does an excellent job making sure the audience understands what's going on at all times, and we begin to know the names of victims, suspects and places that were on screen for only a few minuets, and sometimes never on screen at all.
I will not reveal the end of the film here- an internet search is enough to tell you what happens if you really want to know, but it's impressive that Fincher brought us far enough into the world of these characters that we understand their obsession, and finally support it- we don't want them to stop searching, just for one more clue, one more interview…
Zodiac (2007)