Police brutality remains a persistent social justice problem in many democratic societies. One of the most prominent interventions seeking to deter police abuse is body-worn cameras. Our study is the first field experiment on this issue conducted in a high-violence, developing world setting: Brazil. This paper highlights the daunting challenges to control the police in places where there is a ``war" orientation toward crime and where both supervisors and frontline officers know that what they regularly do in their jobs cannot be scrutinized without seriously incriminating them. Although resistance to turning on body-cameras remained an unresolved problem throughout the study, the very presence of the body-cameras themselves nonetheless induced large changes in police behavior by deterring officers from engaging in armed conflicts and in proactive encounters, including stop-and-searches. However, body-cameras also discouraged police from performing any policing activity, including responding to calls from the community.