A CHICAGO police officer shot and killed a teenager named Laquan McDonald in October of last year, but most of us learned about Mr. McDonald only last week, after a judge ordered the release of police video footage of his death. That is also when prosecutors finally brought first-degree murder charges against the officer. Clearly, such footage has considerable power.

But while protesters have criticized the delayed response to the shooting, no one seems to be asking a more fundamental question: Why were the police in control of the footage in the first place?

Over the past year, as we have seen video after video of police officers killing civilians, many people have argued that greater use of cameras — in particular, police-worn body cameras — could help curb police abuse and mend police-community relations. In May, Attorney General Loretta E. Lynch, in announcing a Justice Department body-camera pilot program, argued that such cameras “hold tremendous promise for enhancing transparency, promoting accountability, and advancing public safety for law enforcement officers and the communities they serve.”

But as currently implemented, body camera programs in the United States too often fail to serve those goals because the police own and control the footage. This is the fox guarding the henhouse. Not only can the police retain footage that they would rather not release; they can also use it for purposes that have nothing to do with transparency and accountability, such as mass surveillance. Until control of this footage is taken away from law enforcement and vested in a neutral third party, with equal access for all interested parties, body cameras will further empower the very party they were designed to check.