Christopher Dorner was a man who had a job as a police officer in California. He was upset and angry because he thought he was treated unfairly by the police department he worked for. He felt like he was discriminated against because of his race and that he was punished for telling the truth about another officer who did something wrong.
Instead of talking about his problems and trying to work things out peacefully, Christopher Dorner decided to do some very bad things. He went and killed some people, including other police officers, and wrote a long letter explaining why he did it.
Other police officers then started looking for Christopher Dorner to stop him from hurting anyone else. Eventually, they found him hiding in a cabin and there was a big shootout. Christopher Dorner died during the shootout.
It's never okay to hurt other people, even if you are mad or upset. It's important to talk about your problems and try to work things out in peaceful ways.