The focus is on the experience of patrol officer David Klinger, who wrote a book in 2004 entitled "Into the Kill Zone." Klinger writes about his experience when he shot and killed a man who was attempting to kill his partner with a knife. He writes that the emotional shock of having killed someone stayed with him for a long time, and it was a major reason for his leaving police work. He is now the chair of the Criminology and Criminal Justice Department at the University of Missouri. He studies various aspects of policing, including the use of deadly force. In a 2002 study supported by the National Institute of Justice (NIJ), Klinger examined the stress a police officer experiences after killing someone in the line of duty. His study is entitled "Police Response to Officer-Involved Shootings." In a recent interview, Klinger noted that police nationally shoot and kill about 1,000 people every year. What has changed, he said, is the presence of social media and the 24-hour news cycle, which has increased public attention to police officers and their killing someone while on duty. Klinger suggests that although police behavior in the field has not changed significantly in recent years, more officers have been incarcerated for shootings on duty. Although reasons for this are still being researched, this circumstance is another factor that contributes to an officer's stress when she/he kills a person.