There is no internet (let alone social media or body cams) during that era, since Jim Crow in America was still being enforced towards black people at that time, but the civil rights movement is gaining traction (since Martin Luther King was alive). I mean, cop violence has been around for a long time before body cams were invented. How did people hear first hand encounters from those victimized back then without reliance on social media?
I don’t know about the 50’s, but my father and his crew of ex-military hippy activists in the 60’s, used to take pictures of the FBI who were trying to infilitrate the groups as agent provocateurs and/or were photographing the protestors to create dossiers. They then posted those pictures, along with the name of the hotel they were staying at on every lamppost in the downtown area. The FBI tucked tail and left after that. This happened during the Vietnam protests in Missoula, Montana.