If there was no recording of the Kelly Thomas beating (which days later caused his death) there would have been 0 justice. Kelly Thomas was a homeless, 135 pound, mentally-ill schizophrenic who was beaten to a pulp by 6 Fullerton, CA police officers. Cops wanted to keep a tight lid on it, so the story really never materialized, UNTIL footage came to light.
I want to trust the cops, but there are bad apples and strong bonds of unity within departments. Trust, but verify as Reagan said, and we can verify with footage, especially when deaths are involved.