As Graysmith, a former Chronicle cartoonist who eventually parlayed his unhealthy fascination with the case into a cottage industry, Jake Gyllenhaal is sufficiently wide-eyed, pouring himself into a fanatical manhunt for the killer who taunted police and reporters like Paul Avery (Robert Downey Jr.) with his infamous letters. Downey’s Avery is well-lubricated and gleefully self-serving, injecting himself into the case with a thrill-seeker’s abandon. That doesn’t sit well with Homicide Inspector Dave Toschi (Mark Ruffalo) – the real-life inspiration for both Dirty Harry and Steve McQueen’s character in Bullitt – but it does open the door for Graysmith, Avery’s overeager sidekick, to take a crack at those confounded letters.

The letters, of course, go a long way toward explaining the mythology that has grown around the Zodiac murders over the years. The Zodiac was hardly the most prolific of serial killers, but like John Doe from Se7en, there was a gruesome theatricality to his methods. He was a master of self-promotion, with his elaborately staged crime scenes, brazen confessions and promises of carnage to come, and Fincher uses the details to great effect in an exhaustively researched epic that is endlessly intriguing without relying on gimmickry.

All of which might come as a surprise to devotees of Se7en and Fight Club, accustomed as they are to Fincher’s own fondness for theatrics. Here, he effectively recreates the paranoia that gripped San Francisco in the time of the Zodiac, but lets the facts of the case speak for themselves and gives the material plenty of room to breathe. His restraint pays off. Zodiac is as lucidly told as James Vanderbilt’s script, faithfully adapted in a way that makes sense of Graysmith’s mysterious characters and labyrinthine subplots and twists. It feels true-to-life, and with that authenticity comes a power that no melodramatics could have provided.

In that sense, Zodiac represents Fincher’s most accomplished work to date – no small praise, considering his deserved reputation as an heir-apparent to Hitchcock. At more than two-and-a-half hours, the film leaves little to the imagination, dutifully exploring every lead while making a convincing (but largely circumstantial) case against Graysmith’s choice as the Zodiac. It is riveting from the start, a compelling stranger-than-fiction story that feels satisfyingly resolved despite the lack of a definitive ending.