When horrorscopes come true ...

David Fincher's magnificently obsessive new film, Zodiac, tracks the story of the serial killer who left dead bodies up and down California in the 1960s and possibly the 1970s, and that of the men who tried to stop him. Set when the Age of Aquarius disappeared into the black hole of the Manson family murders, the film is at once sprawling and tightly constructed, opaque and meticulously detailed. It's part police procedural, part monster movie, a funereal entertainment that is an unexpected repudiation of Fincher's most famous movie, the serial-killer fiction Seven, as well as a testament to this cinematic savant's gifts.

Informed by history and steeped in pulp fiction, Zodiac stars a trio of beauties — Jake Gyllenhaal, Robert Downey Jr. and Mark Ruffalo — all at the top of their performance game and captured in out-of-sight high-definition digital by the cinematographer Harris Savides. Gyllenhaal is the sneaky star of the show as the real-life cartoonist turned writer Robert Graysmith, though he doesn't emerge from the wings until fairly late, after the bodies and the investigations have cooled. A silky, seductive Downey plays Paul Avery, a showboating newspaper reporter who chased the killer in print, while Ruffalo struts his estimable stuff as Dave Toschi, the San Francisco police detective who taught Steve McQueen how to wear a gun in Bullitt and pursued Zodiac close to the ground.

The relative unknown James Vanderbilt wrote the jigsaw-puzzle screenplay, working from Graysmith's exhaustive, exhausting true-crime accounts of the murders and their investigations, Zodiac and Zodiac Unmasked. Graysmith, coyly played by Gyllenhaal as something of an overgrown Hardy Boy, his great big eyes matched by his great big ambition, was a political cartoonist doodling Nixon noses at the San Francisco Chronicle when Zodiac started sending letters and ciphers to the paper, divulging intimate knowledge of the crimes. The first messages arrived in 1969, the year Zodiac shot one young couple and knifed another in separate Northern California counties before moving on to San Francisco, where he put a bullet in the head of a cabbie.

The first cipher stumped an alphabet soup of law enforcement agencies, including the CIA and FBI, but was cracked by a California schoolteacher and his wife. The decoded cipher opened with an ominous and crudely effective flourish: "I like killing people because it is so much fun it is more fun than killing wild game in the forrest because man is the most dangeroue anamal." The letters, the misspellings and the lax punctuation kept coming, and perhaps so did the murders, though only five were substantively linked to him. A publicity hound, Zodiac claimed responsibility for murders he might not have committed, a habit that added to a boogeyman mystery and myth that chroniclers of his crimes, including Graysmith, have exploited.

Fincher made his name with Seven, a thriller in which the grotesquely mutilated bodies of murder victims are nothing more than lovingly designed props. Although more than capable of adding to the exploitation annals, he is up to something profoundly different in this film, which opens with the shooting of two people parked on a lovers' lane at night, an attack that is soon followed by a squirmingly visceral knife assault on a couple during a daytime idyll. By front-loading the violence, Fincher instantly makes it clear just what kind of murderer this was — one who liked to get his hands wet — and ensures that the murders don't become the story's payoff, our reward for all the time stamps, geographic shifts, narrative complication and frustrated action.