Other human rights activists I spoke to worried that citizen journalists like Raull might not even be aware of all the risks they were running. “If the work is intercepted,” Bouckaert told me, “there’s a great danger of people being picked up, jailed, killed. And I do think human rights groups sometimes underestimate the sophistication of the surveillance tools available to governments in some of these areas.” He recalled visiting the office of Abdullah al-Senussi, Libya’s feared intelligence chief, shortly after the overthrow of the Qaddafi government and marveling at the equipment on hand and the extensive dossiers on activists, replete with social-media records and email data.

Several groups have tried to solve the surveillance problem from a technological perspective. Bouckaert is developing a digital-video-preservation vault. Two engineers from the Medical College of Wisconsin, Brian Laning and Bonnie Freudinger, recently won a United States Agency for International Development grant to work on the International Evidence Locker, a free smartphone app. Photos collected on the app are automatically location-, date- and time-stamped, encrypted and securely sent to two separate protected servers, Freudinger told me. They can also be submitted anonymously. Witness is developing its own software, too.

With Witness’s guidance, Raull and his associates had started taking more precautions in their own work. They stopped posting videos in which it was obvious where the video was shot from — from which the police might be able to identify the residence of the shooter, for instance. They had started working in groups. The next step would be to learn how to encrypt files.

The training would be time consuming, Raull said, but worthwhile. “Because the effect multiplies,” he said. “As more people learn about what we’re doing, they’ll send us videos, and we’ll be able to show more of the truth.” He mentioned a plan that he was discussing with Ribeiro to reach out to the young men who drove motorbike taxis in Alemão. The drivers covered large swaths of the favelas every day, and all of them carried smartphones.

Lana said that her mother thought she was “crazy” for associating with Papo Reto, but she told her mother she was proud of what she was doing. “More and more videos appear every day,” she said. “It’s a process. But it’s something good, and the more evidence we can produce, the more we can show the outside world what’s happening here, the better it can get. You can dream.”

It’s not a crazy dream. Last year, a 38-year-old favelado named Cláudia da Silva Ferreira was shot in the neck and torso in Rio’s Complexo da Congonhas favelas during a shootout between the military police and gangs and loaded, unconscious, into the trunk of a patrol car. On the road, the trunk opened and Ferreira’s body tumbled out; she was dragged about 1,000 feet and was pronounced dead shortly after that at a hospital. Another driver filmed the incident with a cellphone camera and sent the video to the local newspaper Extra. Government officials were forced to denounce the actions of the police, and the three officers involved were arrested. They are now awaiting trial.

The International Criminal Court, meanwhile, is conducting investigations in several regions where citizen-produced video evidence could be crucial. In Nigeria, prosecutors are looking into allegations that the militant group Boko Haram has committed crimes against humanity. Already, hours of cellphone footage of the group’s movements have been uploaded to YouTube. And in July, the court upheld a decision to have al-Senussi tried in Libya on charges of murder for his role in putting down the anti-Qaddafi protests. Bouckaert told me that activist footage of the protests would likely be entered as evidence by the prosecution. Similarly, if Assad is ever toppled in Syria and brought to trial, the court will have hundreds of hours of tape to work with.

Two weeks after I returned to the United States, I received an email from Ribeiro. The police and traffickers were again fighting in the alleys of Complexo do Alemão, and the residents of the favelas were spending much of their time indoors. On Facebook, I looked at the most recent work that Papo Reto had posted. In their videos, tracers streaked through the night sky, and platoons of armored police officers marched through the streets. A final photograph showed a boy lying in a hospital bed. Bandages covered his torso; the caption explained that he had been caught in the crossfire, taken a bullet, but survived. “[He] is recovering,” the post read. “Everything will work out!”