A riveting documentary explores the social despair behind a Rio hostage episode

On a June afternoon three years ago, as Rio de Janeiro celebrated the equivalent of Valentine's Day, a homeless junkie named Sandro do Nascimento took a public bus hostage as it threaded through the city's palmiest neighborhood.

To the crush of police and media that surrounded the spectacle, it looked at first as if do Nascimento intended only to relieve the 12 passengers of their wallets.

But during the tense four-hour standoff broadcast live on national television, do Nascimento, a product of the seaside city's notorious favelas, accomplished something that had far greater impact. From the governor down to the random passerby, do Nascimento made the public stare into a face of a social problem that largely had been invisible. His confrontation forced cariocas, as the city's denizens are called, to confront the desperation of poverty and social marginalization.

Bus 174 intercuts news footage with interviews, achieving both heart-stopping urgency and profound reflection. This award-winning documentary by José Padilha and Felipe Lacerda is a model work of nonfiction: It shows us the spectacle of what happened while explaining the many factors why. It is extraordinary in the way it balances the sensational with the sensible.

In news footage, we see do Nascimento through the bus window, pressing his .38 at a 19-year-old female passenger. Will a police sniper take him out? Will a SWAT negotiator talk him down? As we have the tense reactions to this standoff, the filmmakers pause to ask an equally important question: Who is this guy?

Those familiar with the blistering Brazilian films Pixote (1981) or City of God (2002) have witnessed the squalor of the favelas. These makeshift communities built of tin cans and cardboard boxes are cankers on the emerald hilltops overlooking Rio's lapis seaside.

Do Nascimento was born in 1978 near one of the favelas to a single mother, Clarice, whom he would witness brutally knifed to death by robbers when he was 10. From that moment until he took the bus hostage 12 years later, his life was a partial reenactment of that horror with himself as the mugger, though not a killer. He had neither home nor school, was illiterate, and robbed to buy glue to get high.

The one institution do Nascimento was familiar with was the penal system. To give us a flavor of a Rio prison, where the temperature can rise to 120 degrees, the filmmakers take us to one where a cell built for five is crowded with 12 souls who look like the tormented figures in a Bosch painting. To see it in an old master canvas is one thing; to see it in life is unimaginable. The filmmakers make us understand that do Nascimento was treated in a Rio prison in a way most Americans wouldn't treat a rabid dog.

The hijacker had many previous grief encounters with the Rio police, the worst in a 1992 massacre where the cops - woefully underfunded and undertrained, according to the film's talking heads - slaughtered street kids in their sleep.

By providing contexts for the criminal and the crimestoppers, Bus 174 sets the stage for the inevitable tragic climax. Unlike most reality TV, this one does not exploit its characters or audience, but demands our empathy and social action.

Contact movie critic Carrie Rickey at 215-854-5402 or crickey@phillynews.com.

Bus 174 *** 1/2 (out of four stars)

Produced by José Padilha and Marcos Prado, directed by José Padilha and Felipe Lacerda, photography by Marcelo Duarte and Cezar Moraes, music by Sacha Amback and João Nabuco, distributed by Think Film. In Portuguese with subtitles

Running time: 2 hours, 2 mins.

Himself. . . Sandro do Nascimento

Himself. . . Rodrigo Pimentel

Herself. . . Yvonne Bezerra de Mello

Himself. . . Luiz Eduardo Soares

Parent's guide: No MPAA rating (violence, drugs, mature themes)

Playing at: the Ritz Five