[This is technically a reply to various queries and arguments posed/proffered in the comments for my previous post; I'm starting anew because this looks to get lengthy enough that it would likely become unreadable in that little box.]
As promised, then, I went back for another look at the movie, this time making a conscious effort to filter everything through its ardent fans' preferred interpretation. Since I apparently wasn't sufficiently clear last time, or in my formal review, let me note again that this is a very good movie, one that I recommend without hesitation to anyone with even the most remote interest in cinema-as-art. Even on second viewing, its nearly three hours fairly raced by; if I had to describe it in a single non-hyphenated word (thus ruling out "obsessive-compulsive"), that word would be "absorbing." However, I now feel quite confident in my conviction that the whole good-men-destroyed-by-irresolution reading is flatly contradicted by what's actually onscreen. For all its daring in dramatizing a famous unsolved nightmare, Zodiac is ultimately the admiring tale of a dogged young amateur who, by dint of sheer persistence and investigatory elbow grease, ultimately succeeds where the police fail, even if the evidence he's amassed won't cut it in a court of law. (I was reminded this time of the climax of several Agatha Christie novels, in which Poirot lays out his theory of the case but admits that he has no proof apart from the fact that no other explanation is psychologically satisfying; the accused invariably responds with a weary confession.)
Let's consider the last few scenes one at a time.
[Need I warn you of spoilers?]
Graysmith corrals Toschi and gives him an excitable précis of the case against Arthur Leigh Allen. Ignore for the moment that much of what he says is a crock of shit.* What matters is that this litany clearly impresses Toschi, who'd previously been not just skeptical but downright hostile. Ruffalo's entire performance in this scene signifies Grudging Respect. What's more, the exchange that concludes this dialogue comes as close to a thesis statement as anything else in the entire picture.
Toschi (of Graysmith's theory): I can't prove this.
Graysmith: Just because you can't prove something doesn't mean it isn't true.
Guys, I don't know how the movie could get a whole lot more blatant than that. Especially since we've already heard Graysmith tell his [second wife? girlfriend? it's never really specified, is it?] that he's no longer concerned with catching the Zodiac—he just wants to look him in the eye and know that it's him. The movie's epistemological upshot isn't that some things can never be known—it's that knowledge per se must sometimes suffice when evidence fails. Pay close attention also to the sincere gratitude in Toschi's voice as they part, and he thanks Graysmith "for breakfast," twice. Knowing that he had the right guy, even if they never quite managed to nail him, is clearly a huge weight off his back. The last time we see him, he's striding toward his office with renewed purpose. (Or that's what it looked like to me. But even if you think I'm laying it on a bit thick, I maintain that nothing in this final shot of Toschi remotely suggests uncertainty or unease.)
THE HARDWARE STORE
Graysmith looks Evil in the face, and the abyss gazes also, etc. It would have been easy for Gyllenhaal to play this moment with a note of hesitation or uncertainty. He doesn't. Instead, he gives a slight nod, signifying that this encounter satisfies him. He knows it's Allen. I defy anyone to point to any element of this brief scene that suggests an iota of doubt in Graysmith's mind about whether he's drawn the correct conclusion. We see a certain amount of fear, but zero doubt.
THE MAGEAU INTERVIEW
To say that I looked carefully at this scene is an understatement. But first, let me note that the Michael Mageau we see in the film's first few minutes is hardly some iconic golden boy of whose image the '90s Mageau is but a tattered remnant. As a teenager, Mageau (as depicted by this actor) was already skittish and kinda weird; he's visibly nervous well before the Zodiac's car pulls into the Blue Rock Springs parking lot.** This is a minor point, but I mention it because Josh Rothkopf and others have placed a lot of emphasis on what they perceive as the startling transformation of this character, which really doesn't seem very startling to me. He seems like much the same guy, only older and more tired.
Anyway, back to the lineup scene. Sorry, folks, but there's no equivocation to be found here. Mageau looks at the pictures for just a few seconds before pointing at Allen and saying "That's him." At no point thereafter does he waver. He does parenthetically note that the shape of Allen's face, as he recalls it from that night, more closely resembles one of the other men in the lineup, but this detail has no bearing on the identification itself, and Mageau makes that very clear when questioned. (This would be less confusing had he just said something along the lines of "He was fatter then than he is in this picture," rather than using another picture to illustrate the same point.) And people are reading way too much into the words "at least an 8," apparently believing that any answer other than "11" on a scale of 1-10 connotes deep uncertainty. Again, it would have been easy for the actor playing Mageau to depict the ID as hesitant, or for James LeGros (playing Bawart) to look troubled or skeptical. Neither does. "I'm very sure this is the man who shot me" is the last thing Mageau says, and the words ring with conviction. He's clearly leaning toward 9 or 10, merely offering 8 as the worst-case scenario out of prudence, mostly because the shape of Allen's face isn't quite what he remembers.
Not only do they not contradict the indictment of Allen that precedes them, they go out of their way to confirm it. The film allows that a DNA sample failed to match Allen, but undermines this evidence in the same breath by noting (a) the age of the sample in question and (b) that investigators haven't ruled Allen out as a suspect as a result. It reveals that Allen was about to be formally charged, and that only his sudden death "saved" him. Further down, we learn that Allen remains the only viable suspect in the three counties where the Zodiac investigation hasn't yet been officially closed. Finally, we discover that Graysmith's mysterious phone calls ceased altogether after Allen's death. How anyone could find this information self-contradictory or ambiguous I really have no idea; it's about as conclusive as it can be given that there's no real proof. And the reprise of "Hurdy Gurdy Man" over the end credits doesn't negate any of the aforementioned, at least to me. "The narrative effect may be one of closure," Bryant Frazer insists, "but the recurrence of that damned song throws the doors wide open again." To the extent that the Zodiac was never caught, sure. I'm not saying the ending isn't a little creepy. But the movie has a clear resolution: Graysmith figures it out, and is finally content with the knowledge that he is right. See also: both of his books.
Good movie, yes. Postmodern masterpiece, uh-uh.
* Example: The allegedly significant correlation between the Zodiac's silence and Allen's imprisonment on child-molestation charges. In truth, the Zodiac's last confirmed letter was sent months before Allen's conviction, and the 1978 letter sent shortly after his release is now widely considered a fake. (To my mind it's clearly a fake, unless the Zodiac spent the intervening four years attending group therapy and "getting his head straight.")
** I also noticed this time that both screenplay and actress hint that Darlene Ferrin knew, or at least thought she knew, who was following them, which of course supports Graysmith's eventual case against Allen.