When Rio de Paz comes here in force, they clean the cells and bring doctors, and dentists to pull teeth. But Pierre's focus today is on bringing them information, because most of these men have no idea when they will leave this place. Many of them have already been tried, but have been sent here because there is no space for them elsewhere in the overwhelmed system. One man has been here for four years. Others are technically free men, but the word simply hasn't yet trickled down to the administration here. Half the occupants of every cell are lying on bunks or on the floor, eyes rolled back in their heads, comatose from the heat (even outside, it is 41° Celcius). In one cell in the Commando Vermelho wing, there are two men with moist plaster-casts on mangled limbs. An 18-year-old boy shows us a badly broken leg that has not been set properly, crippling him for life. Another man removes his peg-leg, and tells us he has tuberculosis and Aids. An emaciated 60-year-old emerges from the depths of the cell: four months ago, lawyers working for Rio de Paz proved, with fingerprint evidence, that he was innocent, and had this evidence accepted by a judge. In the other wing, there is a man in a wheelchair. When Pierre takes photographs, the men hide their faces in unison. But not captured on camera is the awful way in which they do this, lowering their heads between their knees, or turning towards the wall  — swooning in resignation, misery and shame.

The only other place where the inmates can go is an additional cell with benches along the walls. This is where they receive visitors, and here, among the wives and girlfriends and children, I meet a 33-year-old from Complexo do Alemão, one of Rio's largest and most notorious favelas. He gives his name only as Dilão. In the favela, he commands the men in a particular area and answers to a "general". Here, he is the ranking man in the CV wing. "In the Commando Vermelho, you have to take care of the community. When I am in prison, I have a duty to the 300 men here. If I do something wrong in here, I pay for it on the outside. But I don't, because this is my blood. In the favela, we do what the state should do. The police never come to the top of our hill, but we are there from generation to generation, providing for the community-gas, medicine, repairs. We are not killers. I sell drugs to whoever wants them, I don't tell people to come to my favela." Dilão has been in the drugs business since he was 13. He makes in a day what it would take him a month to earn in a legitimate job, but now he's serving an eight-year sentence. I ask him if it was worth it. "I had 15 years on the street and now I have spent five years in jail. That is the price. Every action has a reaction." I ask him if he would ever leave the drugs trade. "I would like to one day, but it is too late for me now, this is my blood now."

In the opposite corner of the cell, a little girl is dancing with her young father, beaming up at him, her feet planted on his. I ask Dilão about his family. Seventeen of them — his wife, his brother, all his cousins and all his cousins' wives — are in jail for drug dealing. But his four children are "with the church". He wants the straight life for them, and has moved them out of the favela.

Dilão says that the police, "kill people who surrender like putting on a sock". They also sometimes sell captives to other factions to be tortured and killed. This happened to him, but he managed to buy himself out of it with 20,000 reais (about £6,900). I ask him about the UPP initiative. "I wouldn't go out on the streets to commit barbaric crimes like the other factions," he says, "I have no problem, because I would just go to another favela and resume work the same day with the Commando Vermelho there. Or — and why not? — invade one that belongs to one of the other gangs. That's when you see us in 20 cars, with all our weapons. You're going to be seeing that a lot more now. It's too late for the government, we're too powerful. They are doing this UPP now, but it's like paper and fire, an illusion. The past tells us that in a short time all the policemen will be corrupt. There is nothing easier in the world than the corruption of a police officer."

Finally, I ask him a bit more about what he and his friends do for their communities. With all that money, why not pay for some children to go to university? "I take care of my own kids. I can't take care of everyone else's." Dilão grins and shakes my hand warmly. Then he turns to more important business. They want to buy an air-conditioner for their wing, and Pierre has done some research for them. Other men from the Commando Vermelho gather round, and together they frown over his printouts, nodding, calculating and discussing their options.