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Press Release: Will body-worn cameras curb police violence?


Police Constables Yasa Amerat (L) and Craig Pearson pose for a photograph wearing a body-worn video (BWV) camera, before a year-long trial by the Metropolitan police, at Kentish Town in London May 6, 2014.
Photo credit: 
REUTERS/Yui Mok/Pool

This month Stanford researchers are in one of the largest slums – or favelas – in Latin America to launch the first-of-its kind comprehensive study on the use of body-worn cameras by the military police in Rio de Janeiro, Brazil. Over 350 police officers will start wearing cameras clipped to their uniforms during their patrols to record interactions with residents. The yearlong Stanford study aims to determine the effects of this technology on reducing lethal violence, as well as other forms of violent interactions with community members.
Led by Beatriz Magaloni, associate professor of political science and director of the Program on Poverty and Governance (PovGov) at Stanford’s Center on Democracy, Development, and the Rule of Law, this study comes at a significant moment when police brutality is tearing apart the social fabric in communities worldwide, and body-worn cameras are being tested as a way to curb the excessive use of force by law enforcement officials. A study of this nature has never been conducted in a location characterized by extraordinary levels of violence, and the strong presence of armed criminal groups.
“Police-body worn cameras have been adopted in many police departments in the U.S.,” said Magaloni who is also a senior fellow at Stanford’s Freeman Spogli Institute for International Studies. “However, it is not clear how this technology will work in Rio de Janeiro’s context. Even when police officers are instructed to turn on their cameras, we do not know if they will obey. “
To evaluate the use of body-worn cameras, Magaloni established a partnership with TASER International, who is supplying 75 cameras for the study, along with the Military State Police of Rio de Janeiro to introduce this technology in the Rocinha favela. Cameras will be assigned randomly in this study to vary the frequency (number of cameras) and the intensity (hours) of the use of the cameras across territorial police units in the favela.
Magaloni described the two protocols for the use of body-worn cameras that will be explored in the study.
“The first will examine police compliance with the cameras, as some officers will be asked to turn on their cameras during their entire shifts, which is significantly harder to disregard, while others will only turn on their cameras when interacting with citizens, the prevalent practice in the U.S.,” she said.
“Second, the research hopes to contribute towards the development of protocols for the processing of the images, which is a huge challenge for police departments everywhere,” said Magaloni. “It will also help to determine which videos should be audited and what strategies commanders and supervisors can follow to deliver feedback to police officers.”
Rio de Janeiro’s police are considered one of the deadliest in the world. And while this violence has been decreasing since 2008, distrust between the police and favela residents is at a high after the recent police killing of five unarmed young men in Costa Barros, in Rio’s North zone. At the same time, police are being killed at significantly higher rates, which has only further strained their interactions with residents.
Over the past two years, Professor Magaloni and her team at PovGov have been working in partnership with the Military State Police of Rio de Janeiro and the Secretary of Security of Rio de Janeiro to examine the use of lethal force by police officers and the impact of public security efforts in Rio’s favelas. This ongoing relationship has allowed Professor Magaloni unprecedented access to criminal data and police personnel. Detailed analysis of homicide patterns and ammunition usage by police officers, together with the application of surveys and in-depth interviews with police officers and favela residents, have unearthed some of the contextual, individual, and institutional factors that give rise to greater use of deadly force by the police.
As the camera study launches this month in Rio de Janeiro, Magaloni and the PovGov team are hopeful that their research will improve theory and science about police behavior, and provide critical feedback to improve measures aimed at reducing police violence in Brazil and beyond.  

To learn more about the Program on Poverty and Governance, please visit:

Professor Beatriz Magaloni
Stanford Department of Political Science and the Freeman Spogli Institute for International Studies
(650) 724-5949