Rio’s cops are not welcome in favelas like São Carlos. They enter in armored trucks and helicopters, and they have tacit permission to kill: in 2008, they killed an average of three people a day, or one person for every 23 they arrested. In these neighborhoods, the government has virtually no presence, and the city’s three main gangs provide many basic resources, including natural gas and “security.” They also provide a steady stream of victims as they fight each other for control of the drug and arms trades.

This isn’t part of Brazil’s international PR campaign—the beaches, the butts, the good times. But it is the reality of the city that will host the Summer Olympics in 2016. In preparation for the Games, the state government has ordered sweeping changes in the police department, including restructuring its command, improving infrastructure, and increasing pay. More crucial, for the first time the police have begun permanently occupying favelas, dedicating up to 500 officers per neighborhood. But so far only 12 of the roughly 1,000 favelas (some of which are home to 100,000 people) have been secured, and traffickers have migrated to other slums, where the fighting remains as brutal as ever.

“The favelas have a different law, a different economy, and their own defense forces,” says George Howell, the manager of the Rio office of the International Council on Security and Development. “The only way the police can go in is with mega-operations involving hundreds of men. These are incursions into foreign territory.”

Like any occupying army, Rio’s police routinely savage the law. Articles mount in Extra, a tabloid of colorful violence and fleeting celebrity: cops taking bribes, cops dealing drugs, cops selling their guns to traffickers, cops arresting traffickers from one gang and selling them to a rival gang to be tortured and killed. The past two chiefs of the Civil Police are in prison on corruption charges.

One of them is Oliveira’s former boss, who once leaned on Oliveira to solicit money for his political campaign. When Oliveira refused, the chief banished him to a suburban beach community, a career dead end. He returned to Rio only after the chief was arrested.

It is stifling inside CORE’s black armored truck, which the men call “The Skull.” A dozen cops pack tightly against one another on a double-backed bench. Oliveira takes a seat up front. The Skull clears traffic with its siren, leading a convoy of seven police trucks through a neighborhood of patchy vacant lots, towers of trash, and streams clogged with discarded bicycles. “As you can see,” says Flavio Moura, a senior officer seated next to me, “this is not so nice as Copacabana.” Several cops hang their heads and close their eyes. A helicopter flies overhead.

Twenty minutes later, the convoy enters São Carlos, and Oliveira braces himself. He expects to face up to 60 heavily armed traffickers, with only 50 cops. “I’m not here to kill anybody,” he says. “But I’m not here to die.”