A federal judge says the Constitution videoing cops only if it is a "challenge" to their actions.
McDonald's killing and the 13-month delay releasing any video taken by dashboard cameras on squad cars at the scene have led to days of demonstrations.
If an officer is to serve as an eyewitness, will his memory be untainted if he views the footage?
Research shows policy body cams improve public trust, but there are downsides too.
The announcement was part of a three-month inquiry into the militarization of local police following the shooting death of teenager Michael Brown.
Videos are more visceral than any after-the-fact journalism, and hard to deny.