Zodiac opens with the note that the film is based on actual case notes. This distinction makes an important impact on the film. Not making the perusual reference to actual events, and while also taking liberties for dramatic effect and taking time to recreate the era of the crimes, the film is in itself bordering on the obsessive in setting out the minutae of the investigation, cataloguing the progression of time even when there is no real need, so that the audience pores over the evidence as much as the characters. The effect is that we feel the frustration onscreen, hit the brick walls, frown at the bureaucracy and sense the disappointment so that when the time passing onscreen changes from hours to days to weeks to years, we share in the sense of spiraling confusion and likelihood that there will be no answer. This is epitomized in a scene where Jake Gyllenhaal’s character visiting a prisoner linked to the investigation demands she admit to an individuals name, he wants an answer more than anything, even more than the truth, so agonizing has his search been.
Fincher goes big on atmosphere, he always does, fusing a historical recreation and shadow drenched San Francisco, the first part of the film pans around the city in the same gliding fashion the camera does around Jodie Fosters house in ‘Panic Room’, these are not just establishing shots, they are key to imbuing unease and tension. When the ‘certainty’ of the killers actions are gone the tension and questions become psychological, the investigators return to the scene of a crime each anniversary, the passage of time erodes the reason behind their focus, theories are revisited, founded and unfounded. The film does need to keep revisiting the idea of the killer to maintain our anxiety - creeking doors, phone calls, a silly house visit - the commitment of the characters that we meet would I doubt have made wholly entertaining viewing, the natural end to their stories comes in the form of text on screen come the end of the movie, the open ended real life story allows the movie to only go for subtlety in bringing its story to an end. After showing such faithfulness to the progression of the case it could never have sold out in the final reel to finishing with a full stop.