Explaining a mystery is an act of reassurance. It makes us feel that chaos has been defeated, and the forces of order restored. Zodiac, David Fincher's vastly intricate and dazzling drama about the hunt for the serial killer who terrorized the San Francisco Bay Area starting in 1969, offers no such soothing closure, and that's part of what's haunting about it. It spins your head in a new way, luring you into a vortex and then deeper still, fascinating us as much for what we don't know as what we do. Reenacting one of the most infamous ''cold'' cases in U.S. criminal history, Fincher has broken with the fanciful mode of tawdry baroque opulence he employed in Fight Club, Panic Room, and his first serial-killer outing, Seven. Zodiac is based on piles of documents culled from police records, and it's been made in a style of dogged, almost fetishistic realism, its suspense rooted in the scrappiest tidbits of bureaucratic protocol. Fincher refuses to squeeze the hunt for the Zodiac killer into tidy arcs. The revelations occur where they did, and not where they didn't.
In this movie, it's the killer who imposes order on things. As we watch, two young people, parked on a lovers' lane, are assaulted by a stranger who pulls up in his Mustang, then fires a hail of bullets. Weeks later, a letter appears in the offices of the San Francisco Chronicle. It's a confession, written in blocky letters, with details only the killer would know, and signed with a logo that looks like a rifle sight; it also includes a page written in cipher code. Will cracking the code reveal the killer's identity? (A high school teacher soon solves it. Answer no.) The Zodiac, as he christens himself, is a madman who promises to kill again, but his ruthlessness is surpassed by his ingenuity as a new kind of urban sociopathic media terrorist.
A procedural thriller for the information age, Zodiac focuses on the complicated efforts by a handful of investigators to uncover his identity. There's the Chronicle's star crime reporter, Paul Avery, played by Robert Downey Jr. as a talented drunken flake who mouths off to superiors in a way that reminds you what newspaper journalists were once like, and there's Robert Graysmith (Jake Gyllenhaal), the paper's political cartoonist, who kibitzes on the case for no good reason except that he's a moody, hyper-curious lurker with a thing for puzzles. (The movie is based on two books by Graysmith.) There's Dave Toschi (Mark Ruffalo), a homicide inspector more earnest than inspired, and his low-key partner, William Armstrong (Anthony Edwards). Legally, the detectives have to coordinate almost every move with the surrounding districts (Napa, Vallejo), and the result is a communication tangle that's one of the movie's sly themes the way that information gets lost in a bureaucratic state.
Re-creating the pre-tech grittiness of the '70s, Fincher doesn't just get the cars and Top 40 tunes right. He gets the smoke-clogged offices with their blinking telephones, the ugly wood paneling and, more than that, the dawn of the tabloid age, when a serial killer could still set off shock waves. At times, we might be watching a film by Sidney Lumet in his high fluorescent period, or maybe the All the President's Men of deranged homicide. We see most of the Zodiac's murders, and they are coldly horrific to behold (especially the stabbing of one couple by a lake), but the real story is the way that the killer uses the mass media to inflate the dark grandeur of his crimes. He creates a myth of himself, like Jack the Ripper or Charles Manson, and once that myth takes on a life of its own, it's not even clear that the murders he's bragging about are all his. (There's no pattern to them.) The cops and reporters are looking for a killer, but they're also chasing a ghost.
Zodiac never veers from its stoically gripping, police-blotter tone, yet it begins to take on the quality of a dream. It's an analogue of the post-9/11 world, where the enemy is specific yet, by virtue of his self-projection, omnipresent, and therefore impossible to pin down. As the '70s roll forward, the investigators move on to other cases, but Graysmith, the amateur, can't, and Gyllenhaal, who marinates his boyishness in quivery tension, makes that obsession ours. Slithering into police libraries, interviewing suspects, tearing his family life apart, he's eaten up by the need to know, and he makes connections no one else does, but does he solve the case? By the time he fastens on to a monster, maybe the monster (and maybe not), Zodiac leaves us haunted by the knowledge that he's looking for something that can't be found: a way to make the monsters go away.