Casey Affleck, left, and Brad Pitt star in "The Assassination of Jesse James by the Coward Robert Ford." The Western opened in theaters on Friday.

Who knew it took Jesse James this long to die?

Andrew Dominick's somber, sober and seemingly well-researched Western is a film that plays as long as its title — "The Assassination of Jesse James by the Coward Robert Ford."

We know what's coming, but Dominick takes his own sweet time getting us there.

"Assassination," based on a Ron Hansen novel, re-imagines this legendary piece of Western lore as a Jesus-Judas tale of betrayal. Dominick's film rides on the back of Casey Affleck as the boyish, hero-worshipping Robert Ford, a late addition to Jesse's circle and, it turned out, a fatal one.

In early scenes, Affleck-as-Ford all but begs first Frank James (Sam Shepard), then Jesse (Brad Pitt), to let him be their "sidekick."

"I honestly believe I'm destined for great things," he assures them as their eyes roll and patience runs out.

Ford, younger brother to the always-laughing Charley Ford (Sam Rockwell), isn't taken seriously. He bears each new insult from Jesse with sheepish good humor. But we know better.

As Jesse, Pitt wears the dark clothes and shows the weariness of an outlaw who hasn't really realized that he has aged out of his career of train and bank robberies. At 34 (Pitt is 44), Jesse has a wife (Mary Louise Parker, with little to play here), children and a secret "cattleman" identity that he wears in the various towns where he lives.But Jesse has gotten sloppy. The film's opening train robbery, his last (in 1881), is both ruthless and inept. Jesse has, the ever-present narrator (Hugh Ross) says, run out of reliable "sidekicks."Ford's motivations are thoroughly explored. He has bought into Jesse's rebel "Last Holdout of the Confederacy" mythology. He craves a myth all his own. And while he fears the man as much as the members of this gang that can't shoot straight, he is the most disillusioned by the real Jesse.Pitt's James is a cryptic figure, capable of terrible, unexpected violence — utterly paranoid as a man on the run might be. It's an engaging, mysterious performance that gets by mostly on Pitt's charisma.For those craving a view of how dark and crowded railroad cars really were, what bad shots most of these pistol-packers were, or awed by the sight of dangerous men in buffalo coats riding through knee-deep snow, it's a view of the West beyond the myth that's worth enduring, if not relishing.