Two years before Zodiac, Capote depicted Truman Capote making a fuss about possibly not having an ending for his seminal true crime novel, In Cold Blood. Robert Graysmith, on whose so-called non-fiction books Zodiac is based, had no such qualms about playing the speculation game, nor did director David Fincher.
The comparison may be unfair, though. Graysmith is no Capote (but then, who is?), and In Cold Blood isn’t a whodunit — though technically neither is Zodiac; after more than two hours, the takeaway is not so much ‘who done it’ as ‘who a very small and not quite persuasive group of people think done it.’
In a nutshell, this is a movie about a hunch. The film would work better (and that’s not to say it doesn’t work at all) if it were, like Capote, about a man obsessed with a crime rather than with the criminal — especially considering that the Zodiac killings constitute arguably the most famous unsolved murder case in American history with no shortage of suspects, which means the perpetrator provides a blank space that quote-unquote investigators such as Graysmith can fill with their cherry-picked theories, moving them around until they fit their preconceived notions.
Unfortunately, Fincher is what James Randi would have called a true believer, and Zodiac leaves little doubt that the director is as certain that Arthur Leigh Allen (John Carroll Lynch) was the Zodiac as he is that Herman Mankiewicz singlehandedly wrote Citizen Kane.
Fincher expected us to take this on faith, though, and the absence of concrete evidence may raise doubts about the narrative’s objectivity (or lack thereof) and frustrate viewers looking for an unbiased approach.
That said, Zodiac is a better movie than Mank because Fincher was more in possession of his faculties in 2007 than in 2020. Accordingly, the former film makes a more coherent and convincing case for its far-out thesis than does the latter (and even this we can attribute to the credibility of a very deep roster of strong supporting players, in addition to a rock-solid core of leading men with character actor chops in the most prominent roles), although it still boils down to a ‘what if?’ scenario.
So flimsy in fact is the entire house of cards that the story ends — or rather comes to a halt (lacking, as it does, a logical conclusion) — on a fallacious note that applies to pretty much absolutely every crackpot ad hoc hypothesis ever: “Just because you can’t prove it doesn’t mean it’s not true.” It’d be a lot more reassuring if you could, though.