http://www.slate.com/articles/news_and_politics/crime/2015/05/police_shootings_the_grim_videos_cops_watch_of_their_colleagues_being_killed.html

In recent months, videos in which police officers are seen using lethal force against civilians have become disturbingly common. It’s a grim new canon of violence: Walter Scott shot in the back in South Carolina; Eric Garner struggling to breathe on the streets of Staten Island; Tamir Rice losing his life over a toy gun in Cleveland; Kajieme Powell crumpling to the ground in St. Louis. The videos have become reference points in the national debate over policing, and a catalyst for a political movement to reform police tactics and training. They have undoubtedly changed the way large swaths of Americans view law enforcement.