Don't listen to anyone who tells you that David Fincher's new movie is too long or that its ending will leave you unsatisfied. Lots of the film's early notices read like reviews of a restaurant where the service was slow and the waitstaff never got around to bringing dessert. Zodiac, to the contrary, is a masterfully made anti-procedural that's fascinating from start to finish.

The absence of resolution, of traditional narrative closure, is the whole point here. The serial killer who terrorized the San Francisco Bay area for several years beginning in the late 1960s, and who referred to himself in letters he sent to the press as the Zodiac, was never caught. The filmmaker who gave us The Game, Seven and Fight Club has undertaken a mystery of the most unconventional kind. Rather than watching as clues are assembled and a solution is found, we look on as four men assemble clues and find only that their lives and careers are destroyed to varying degrees by their obsession with the case.

The film is a sort of forensic All the President's Men. Robert Downey and Jake Gyllenhaal play San Francisco Chronicle coworkers. As Paul Avery, Downey covers the paper's crime beat and struggles with addictions to drugs and alcohol. (How's that for savvy casting? And it's not even the picture's savviest.) Gyllenhaal's the daily's cartoonist, Robert Graysmith, a former Eagle Scout who finds himself inexplicably compelled to unravel the riddle. The script is based on the two bestsellers he went on to write.

Soon after two teenagers on a date are shot in 1968, newspapers including the Chronicle started receiving taunting letters containing cryptic encoded messages. The killer demanded the papers publish his communiqués and they complied, making him one of the most famous and feared figures in the country. More killings followed, along with more letters and thousands of leads that seemed to go nowhere.

On the law enforcement side of things, police were as baffled as were reporters. Their investigations led to similar dead ends. Anthony Edwards and Mark Ruffalo portray homicide detectives William Armstrong and Dave Toschi. The former ultimately left the force in large part due to frustrations with the Zodiac case. The latter stuck it out as the investigation dragged on for decades, long after the murders had stopped. At one point, the killer had authorities so turned around that Toschi himself even came under suspicion for having penned one of the madman's missives.

All the key players do finely tuned, immensely watchable work. Fincher employs a newly subdued approach that eschews flashiness in favor of character study and information flow. It's a truly audacious experiment, and he pulls it off with mood and suspense to spare. He also comes as close to solving the mystery as anyone ever has, having unearthed new clues in the course of his preparations. He's the perfect director to tell the story of these obsessed men. As it turns out, he's one of them.

As for that savviest bit of casting: Think of the sweetest, least threatening male movie role in the last couple of decades and you might recall the cherubic face of John Carroll Lynch, who played Frances McDormand's stamp-designing husband in Fargo. The director picked him to play the late Arthur Leigh Allen, the man experts consider the suspect most likely to have been the Zodiac. Great choice. Chilling performance. A dead ringer for Allen, he looks like the last person who'd commit these crimes. Which, if he did, may be why he got away with murder.