Because Zodiac takes as its subject one of the most notorious serial killers in American history, and because its director, David Fincher, remains best known for Se7en, a movie about one of the most diabolical serial killers in film history, most people will naturally assume that what we have here is a picture about a serial killer. This assumption will sell tickets, no doubt, luring the unsuspecting viewer into one of the most radically ambitious and conceptually bizarre projects ever released by a major studio. If you're even slightly familiar with the case, it will dawn on you at the end of Zodiac's first hour that no additional murders are forthcoming—the Zodiac killed only five people that we know about for sure, all of them between December 1968 and October 1969—and that even the taunting letters and ciphers that made him infamous are about to cease without explanation. You also know that the Zodiac was never caught, and that you've signed on for a film that runs closer to three hours than two. Where can they possibly take this story? you will wonder. Only when you realize that the movie's pace is speeding up in inverse proportion to the killer's activity, however, will you understand that you're actually watching the most exhaustive portrait of obsessive-compulsive disorder ever seen onscreen.

Odds are, of course, that you're not already familiar with every detail of the Zodiac case. Never fear—after seeing this movie, you will be. Adapted from two books by editorial cartoonist-turned-amateur sleuth Robert Graysmith, Zodiac features a handful of ostensible characters: Graysmith himself, who worked at the San Francisco Chronicle during the period when the Zodiac was sending letters there, is played by Jake Gyllenhaal, and we also spend significant face time with star Chronicle reporter Paul Avery (Robert Downey Jr.) and legendary SFPD detective Dave Toschi (Mark Ruffalo). But none of these three men, nor anything that you could credibly call human drama, amounts to much more than a ripple in Zodiac's endless, raging sea of investigative minutiae. Dates, times, locations, statements, interviews, clues, totems, theories—Zodiac is less narrative than avalanche, opening crevasses in characters' and viewers' psyches alike. Even as Avery sinks into alcoholism and Graysmith's obsession with the case destroys his marriage, it's the mental state of the filmmakers that seems troubling. Existentially horrified by the absence of certitude, the movie, like Graysmith's books, drastically overcompensates via maniacal attention to detail, which manifests as a desperate need to embrace What Is Known.

Of course, Fincher is still Fincher, so it's not as if any of this plays as dry or bureaucratic. Scene by scene, Zodiac is the director's most visually restrained work to date, taking its cue from the mostly functional mise-en-scène of the police procedural; at the same time, he can't resist the occasional expressionistic flourish, as when two young lovers en route to violent death drive slowly down a quiet Vallejo street as fireworks explode overhead. (The Zodiac's second attack took place on July 4, 1969.) Nor will you ever again be able to listen to Donovan's loping "Hurdy Gurdy Man" without a chill running down your spine, assuming that you can now. The actors, for their part, do a credible job of creating the necessary illusion that they're playing human beings rather than walking, talking DSM-IV codes: Downey turns Avery, who received several personal communiqués from the killer, into his standard hilarious motormouthed cynic, while Ruffalo, playing the real cop who inspired Steve McQueen's character in Bullitt, expertly mimics Toschi's shaggy, understated demeanor.