Zodiac; Black Snake Moan

Length matters. The running time of Zodiac may well be a function of its subject -­ 156 minutes to span more than two decades, from the late 1960's to the early 1990's, when a serial killer who called himself Zodiac terrorized the San Francisco Bay Area and taunted his pursuers with coded messages. And though the killer was never found, the scope of David Fincher's beautifully crafted film goes beyond the pursuit to the erratic nature of the investigation -­ an investigation that became an obsession for two cops and two newspapermen in San Francisco. Obsession is the real subject here, and obsessing about anything briskly doesn't count. But the film also feels self-obsessed -- it's an intriguing drama that slowly devolves into a bleak meditation on the absence of dramatics.

Zodiac was adapted from the book of the same name by Robert Graysmith. He was a political cartoonist at the San Francisco Chronicle when the case hit the news. In fact, the Chronicle was part of the news, one of three papers to which the killer first sent letters boasting of his crimes. That makes the film as much a newspaper story as a police procedural. One of the two ink-stained wretches of this piece is Graysmith himself, who's played by Jake Gyllenhaal ­ Bobby is a relative novice with a nerdy demeanor who's treated like a clueless intern. The other is the Chronicle's crime reporter, Paul Avery, a deep-dyed cynic, but, in the hands of Robert Downey Jr., a man whose mordant wit provides welcome relief from the film's oppressive tone.

The cops, played by Mark Ruffalo and Anthony Edwards, operate in a parallel universe. They struggle to pull together evidence from Bay Area police forces and jurisdictions that barely communicate with one another, while the Chronicle guys second-guess them, follow their own leads and get in the way. Altogether, you have a sense of intelligent, highly motivated men making their way through endless mazes of clues, intuitions, misapprehensions and misinformation.

The performances are uniformly fine ­ low-key for the cops, steady- state acidulous for Downey and increasingly intense for Gyllenhaal's Bobby, a nerd who comes from behind to dominate the proceedings with his gift for ciphers and solitude. Yet the overall style is quite conventional, and a vital energy is missing throughout, except in Brian Cox's sly, shrewd performance as the celebrity lawyer Melvin Belli. This silver-haired popinjay is self-absorbed to the nth degree, but he's larger than life, and a wonderfully shameless self- dramatizer.

Craig Brewer's Black Snake Moan is nothing if not ripe -- and provocative, at least until you see it. A black man stands menacingly over a white girl in the publicity stills; he's holding one end of a massive chain that encircles her waist. But you can't judge a potboiler by its lid. Yes, Christina Ricci's Rae is the town whore, and yes, Samuel L. Jackson's Lazarus has his bitter side; a former bluesman, he's got the blues since his young wife left him. But when the church-going Laz tells the bed-going Rae, "I'm gonna cure you of your wickedness," you'd better believe that the emphasis is on a cure. She's been abused, he's been wounded. He fixes her, she fixes him and they redeem each other. Craig Brewer's debut film, Hustle and Flow, celebrated a good-hearted pimp. Now his second feature is a soft-core substitute with a heart of gold. For all the preposterous clichés of the plot, Black Snake Moan finds unchained energy in its foolishness, and gives Jackson a chance to pluck a guitar and sing. He's really good at it, too. The music almost redeems the movie.