In November 2019, Arian McCree raced out of a South Carolina Walmart after he was placed in handcuffs for allegedly stealing a $45 lock, police said. But exactly what happened next remains unclear, in part because the responding officers didn't activate their body cameras until after McCree was gunned down in a hail of police bullets.

Body cameras have been hailed as a key tool in enhancing transparency in policing and providing crucial information in use-of-force incidents, but having them doesn't mean they'll be used properly. Examining the body camera policies of 28 large police departments in the United States, NBC News found more than half have not implemented three basic rules experts say would allow cameras to be effective.