As everybody knows, America is obsessed with killers. I shall prove this with the following two lists:

-John Wayne Gacy, Charles Manson, Jeffrey Dahmer, Ted Bundy

-William B. Saxbe, Ramsey Clark, Richard Thornburgh, Edward Levi

What do the four names in each set have in common? If you said "the first four are serial killers, and the second four are US Attorneys General,"* congratulations! But be honest, which took you longer to figure out?

As a reflection of this grim national pastime, our pop culture is positively saturated with killers and serial killers and the dour cops who take them down. Our televisions are heavy with CSI and Law & Order spin-offs. We like crime, and we always have.

There are many reasons why David Fincher's Zodiac is a good or even great film, but the reason that it's a full-fledged masterpiece is because of its focus, not on the wave of killings in the San Francisco Bay Area in 1968 and 1969 or on the paranoia that gripped the city (although those are both prominent), but on the people who grow obsessed with those killings and that paranoia. It is a study of the fringe elements of a society that already privileges the fame of serial killers of the fame of Attorneys General. Which is to say that in a world gone mad, there always has to be someone madder.

The shortest conceivable precis of the Zodiac killings: starting in December of '68, five people were killed and two people critically wounded by a man who in July of '69 began sending letters to the San Francisco Chronicle, the San Francisco Examiner and the Vallejo Times-Herald, taking credit for the murders and dropping all sorts of bizarre literary references, misspellings and cryptograms into his messages. Zodiac picks up after the second attacks, days before the letters began, and chiefly concerns three men: Paul Avery (Robert Downey, Jr.), the Chronicle reporter who chiefly turned the Zodiac into a media star; David Toschi (Mark Ruffalo), the SFPD inspector assigned to the case; and Robert Graysmith (Jake Gyllenhaal), a Chronicle cartoonist whose fixation on the Zodiac would ultimately wreck his home life and culminate in two books that rather hyperbolically claim to "solve" a still-unsolved case, newly reopened by the SFPD.

In point of fact, the movie is based on Graysmith's books, and you might think (certainly I did, going into it), that Fincher and screenwriter James Vanderbilt would lionise the author and validate his every claim. Nothing of the sort happens. The movie never really gets around to forming an opinion of Graysmith's favored suspect (it couldn't be easier to find that info out online, so I'll not mention it, in deference to the spoilerphobic), and Graysmith himself is made out to be delusional, paranoid, destructive and pathetic. This despite being played by the immensely likable Gyllenhaal, who tones down the character to being a banal little nothing of a person.

All this is such a bitter slap in the face to procedural-obsessed audience; everything is done right and logically put together and evidence is pored over, and no answer ever comes to light. That's crime-solving, boys and girls. At one point, Toschi thinks he has the killer, until handwriting analysis comes back negative. "I don't know if I'm disappointed because I thought we had the right guy, or because I just wanted it to be over," he sighs, and Ruffalo's performance makes it entirely clear that he really just wanted it to be over. A neat little bow on the third-act resolution, all well with the world, the killer behind bars and the boy gets the girl.

Graysmith wants something completely different. He makes it clear late in the film that he's not gunning to put the Zodiac behind bars, although that would be nice, he wants to look at the Zodiac and have the killer know that he, Graysmith, knows. He wants to be the first one to solve the puzzle, the person who for a brief moment is the only one in the world who knows the secret of the Zodiac. He wants to watch huge piles of evidence fall together in the cleverest way he can imagine. It's all about Robert Graysmith and his incredible brain, and the pride of figuring it out.

Prior to seeing the movie, I spent a couple nights researching the case, about which I knew nothing, on the assumption that the film would be much more of a docudrama than it is. And in seven or eight hours, I learned more than any reasonable person of healthy mind could conceivably wish to know about the Zodiac, and despite that, I am not by any possible definition, a "Zodiac expert." I lurked on message boards full of "Zodiac experts," and they are intense people with libraries of information committed to memory, people who spend days and days arguing with glee over the tiniest minutiae. Perhaps they truly expect to solve the case, I do not know, but mostly it just seems like they delight in thinking about endless useless facts. For all I know, all of them lead rich and full lives, but they evince a knowledge of the Zodiac that puts my rabid cinephilia to shame. I don't know how they would have time for anything else. Robert Graysmith, in the movie, is just like them. His whole life becomes the Zodiac - his life is ruined - and to take away the pain of leading a ruined life, he focuses more obsessively on - the Zodiac.

Yet it's not confusing. We do not ask of Graysmith, "why does he care?" in the way that we would if he wrecked himself on obsessively collecting first editions of Trollope or re-orchestrating Bach music for trumpet and snare drum. Serial killers are fascinating, and the true obsessives aren't unlike us, they're just us taken to a farther degree.

Dear Lord, a thousand words and I haven't even hinted about what else makes Zodiac great. Well, to start, David Fincher has finally worked out his need for all of his movies to be kewl, where the tics and fidgets of style tended to overwhelm theme and art (the neatest example: 12 years ago, he directed a serial killer film titled Se7en, which I find very well made and hard to watch, and which is largely just death porn, all about the awesome gore effects and awesome gloom and awesomely nihilistic twist ending. It is indeed the precise opposite of Zodiac in this way). He's always been an extraordinary craftsman in search of a healthy lesson in restraint. With Zodiac, he finds restraint, and I do not mean that he is sedate and austere, but that every choice made is made to further the thematic goals of the whole. Indeed, many shots are bravura exercises in showing off, but always for a reason. Little is wasted, and even the 158 minute running time is not only earned but vital, stretching out the years and reminding us of the sheer man-hours invested in this colossal dead-end. And the length allows Fincher to stage and restage variations of scenes, turning the structure of the film into a kind of symphony, where tiny differences between this handwriting scene and that handwriting scene take on huge weight.

And it looks simply fantastic. I could get into a whole thing about how it was shot on a Thomson Viper, the first major Hollywood project ever, and your eyes would glaze over, especially when I get to the part about how I totally want to shoot my oft-delayed upcoming project on a Viper now. So instead I will just say: brown. Much brown. If it had been shot on film, I'd have said that the entire reel was kept in room full of nicotine smoke. It's so filthy looking, and I can't begin to explain how that's perfectly right. But it is.

God, the whole film is perfectly right. It's March, so "teh best film of teh year!!!" means nothing. But it's a masterpiece nonetheless. It is a flawless, wonderful masterpiece about the dark side of American celebrity culture, and it's a strong argument all by its lonesome that 2007 is already a better year for movies than 2006.

*Specifically, the US Attorneys General at the time of each respective killer's period of greatest activity.