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Open Access Publications from the University of California

Warriors and Vigilantes as Police Officers: Evidence from a field experiment with body-cameras in Rio de Janeiro


We present the first randomized experiment on police body-cameras in a high-violence setting: Brazil. Camera assignment reduced stop-and-searches and other forms of potentially aggressive interactions with civilians. Cameras also produced a strong de-policing effect, where police wearing cameras were significantly less likely to engage in any form of activity, including responding to requests of help. These changes in police behavior took place even when most officers refused to turn their cameras on when interacting with civilians. Low levels of compliance suggest that this technology in itself is no solution to police brutality. To address this problem, during part of the study we randomly assigned cameras to supervisors and this had a strong effect on frontline officer’s behavior, significantly increasing their policing activities. Police surveys, interviews, and focus group reveal that the organizational culture that perpetuates police violence is a strong factor explaining why officers appear to have sabotaged the cameras.

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