I actually sort of agree with semck, especially in this sense;
Even if police body cams were ubiquitous and live streamed to the public or something, it would do nothing to address the underlying problem that Black Lives Matter is protesting: the police in America are not part of the communities they police - they seem them as the enemy and worse, are often explicitly racist against them. As I posted recently we are now even hearing that white supremacist hate groups are intentionally infiltrating the police.
While body cams could help to solve certain surface level problems, they will not solve racist policing; they will not solve illegitimate policing, they will not solve the oppressor/oppressed relationship that the citizenry currently has with their police forces. At core what is wrong with our police is their philosophy of policing. That's not a popular critique to make, more popular is to suggest a new technology can solve it, but we will find I am sure, we we always find in such cases, that it will be "improved means to an unimproved end," with its own set of problems and not really solving the first set.
In my opinion it goes even further than the philosophy of policing. It's about democracy. In a country with a democratic deficit such as the United States, the police becomes the agents of the unelected elites. They enforce their laws, and do not protect the interests of the public. No surprise, then; when their supposed job of protecting us from real threats begins to play second fiddle or even becomes irrelevant (people in New Orleans rarely even bother to call 911, doubly so if they are black).
Eric Garner, remember, was killed for selling loose cigarettes. The people in the community he was part of have no problen with selling loose cigarettes. Yet the police enforced the law of the land; which is increasingly unjust, the laws being made by elites and not by the people.
So that's the *real* underlying problem. Till you fix that, expect more riots, protests, and police brutality.