If the cameras exonerated the police we would have seen the video by now.
This is called ‘circling the wagons...
No, we would not. Costco would not want to release video of their customers being shot. The police would not want to voluntarily show video of their shooting of an entire family of unarmed shoppers. And lawyers from all sides would have a say in the matter. Also there is no generic right of the public to see every video.