Growing up in the Bay area, David Fincher's first exposure to the serial murderer known as the Zodiac Killer came during childhood, when shadowy notions of monster men and the harm they intend loom larger than they ever will again. Though it is noted at the outset of Zodiac that the following is "based on case files" from the actual murder investigations, Fincher's latest film is more potent as a draught from that spooky pocket of closet, where the bad things are. Fusing components of the serial killer genre, police procedural, talky '70s city flicks and Fincher's own impressionistic, vividly inflected sensibility, Zodiac is most coherent as an evocation of that shapeless threat: the strange and terrible; the unseen and unknown; and its incompatibility with the adult reflex to reason and research it into submission -- to solve. The bogeyman never really goes away, and for a small fleet of men in Zodiac (including Fincher, who has cited the film as his most personal), a series of California killings and the letter-perfect personification of their perpetrator re-opens that long-ago closet, triggering a retaliatory avalanche of wordy brainpower in the quest for containment, satisfaction, conviction.

Screenwriter James Vanderbilt adapted the two books on the killings (Zodiac and Zodiac Unmasked) written by Robert Graysmith, an editorial cartoonist at the San Francisco Chronicle when the murderer sent his first letter and encrypted message to the paper on Aug. 1, 1969. For Graysmith (played here by Jake Gyllenhaal), the case's drama, along with the coded ciphers, are immediately compelling, and he takes a bystander's interest on the fabulously rendered floor of the Chronicle's newsroom; crime reporter Paul Avery (Robert Downey Jr. in a zippy ascot, frisky and fallow) continually snaps at Graysmith for "looming" over his desk.

The Solano county shooting homicide that opens the film (a powerful, perfectly calibrated scene) barely made the blotter in San Francisco, but when the first letter arrives at the Chronicle, with the author threatening to kill again if his letter (and the cipher that purportedly held the key to his identity) is not published, the staff is mobilized and even the laconic Avery swings into action. While Graysmith solves part of the first cipher, revealing its manhunting reference to the 1932 film The Most Dangerous Game, for the first two-thirds of the film Fincher has Gyllenhaal literally looming in the background, as two more murders occur and the letters keep coming, one threatening to pick off schoolchildren as they step off the bus.

The San Francisco police, of course, are interested in the Chronicle's new pen pal, and inspectors David Toschi (Mark Ruffalo, affecting a whispery deadpan) and William Armstrong (Anthony Edwards, aloha!) are on the job. Dermot Mulroney, Donal Logue, Philip Baker Hall and Brian Cox are among the deep-voiced, manly men in shirtsleeves and ugly ties all involved, in some capacity, with the case. Toschi runs into old-school problems almost immediately: information is unshared and inconsistent between jurisdictions, and this sets up a domino effect of oversights that is one of the most problematic aspects of the narrative. There are survivors from two of the crime scenes, and one of them, who ends up matter-of-factly identifying the killer 22 years later, when someone thinks to ask him, is allowed to simply disappear; buried in thousands of leads, the detectives seem to look past the obvious, stalled in a morass of information.

Zodiac skirts a similar fate, as Fincher follows as many of the case's trails as possible -- even the ones that turn cold or prove empty. Several trademark bravura sequences compress and overlay all the words, talk and conjecture with the slickness and momentum we expect, and the film jumps ahead by hours, then weeks, then months and years. Yet at over two-and-a-half hours of dead-ends and bedevilment, there doesn't seem to be enough intrigue or, alternately, involvement with the characters to justify the empirical extents Fincher is intent on mapping.

Graysmith's obsession seems to be the cornerstone of the film -- the others at least have the excuse of doing their jobs, and there are hundreds of unsolved murders every year --and yet when his wife (played by Chloë Sevigny) demands, on her way out the door with the kids, what, exactly, his Zodiac-addled damage is, he answers simply "I need to know who he is." Graysmith eventually reconnects with Toschi and falls into a few circumstantial rabbit holes before making his way back to Arthur Leigh Allen, a sex offender whom the inspector reluctantly cleared on a handwriting technicality in 1971. "Just because you can't prove it doesn’t mean it isn't true," Graysmith tells Toschi, his eyes glittering, and it's as airtight an argument for the existence of the bogeyman (perhaps the most successfully realized character in the film) as it is for the guilt of Allen, which itself ceased to matter in the world of Zodiac when he slipped away years before. (The truth cannot always transcend the facts, and we are told in some final title cards that Allen eluded arrest until his death in 1992, when evidence was finally being compiled against him, and the case remains open.)

The principals in the case remain convinced that Allen was their man, but resolution is rendered irrelevant when Zodiac inverts itself into a sort of anti-procedural, and "I need to know who he is" becomes more of a cry in the dark than a convincing rationale. I don't know about you, but as a child I wouldn't look in my closet at night for all the cookies in Candyland; I already knew he was there, I didn't particularly need to know who he was. Fincher taps into this rich, inky vein of dread and paranoia using just the facts (though I have to doubt anyone said "Do the math," as one character does, in 1970), leaving the killer -- portrayed in the murder scenes by three different men -- with his fangs intact for the next generation.