Police officers in Ferguson, Missouri, have started wearing body cameras weeks after a cop shot dead an unarmed teenager during a confrontation. The recording devices were first used at a Saturday march protesting the death of Michael Brown, and training for the entire police force is nearly complete, officials told NBC affiliate KSDK. Two private security firms donated the cameras amid an uproar over police tactics in the St. Louis suburb.

More than 1,000 police departments around the country use similar cameras. Despite some privacy concerns, the gadgets have won the support of law-enforcement officials and civil libertarians. In Celina, Texas, which began equipping officers with the $300 devices nine months ago, police brass say it's a crucial tool because it captures exactly what the officer sees when interacting with a suspect. "Documentation, accountability, transparency is part of what we do now, and it should be," Chief Mark Metdker told NBC News.