John M. Darley

John M. Darley (April 3, 1938 – August 31, 2018) was an American social psychologist and professor of Psychology and Public Affairs at Princeton University. Darley is best known, in collaboration with Bibb Latané, for developing theories that aim to explain why people might not intervene (i.e. offer aid) at the scene of an emergency when others are present; this phenomenon is known as the Bystander Effect. This work stemmed from the tragic case of Kitty Genovese, a New Yorker who was murdered in March 1964 while 38 people either witnessed or heard her struggling with the assailant. Darley also studied the effect of assessment on performance and proposed Darley's Law, which states that “The more any quantitative performance measure is used to determine an individual’s rewards, the more subject it will be to corruption pressures and the more it will distort the action and thought patterns of those it is intended to monitor.” 
Life and career.
John M. Darley was born on April 3, 1938 in Minneapolis, Minnesota to father John G. “Jack” Darley, a counseling psychologist known for work in student personnel psychology, individual differences, and psychological testing.
During the last decade of his career, he also worked in the psychology department at the Princeton (formerly Woodrow Wilson) School of Public and International Affairs and retired from the Princeton faculty in 2012, accepting emeritus status.
Darley died August 31, 2018, He is survived by his widow, Genevieve Pere, former spouse Susan Darley, two daughters, and three wonderful grandchildren.
Research.
While in New York, Darley began the research that defined his career. After hearing of the tragic case of Kitty Genovese, he was inspired to explore why people are less likely to intervene when there are other witnesses present, a phenomenon is the “Bystander effect”. With collaborator, Bibb Latané from Columbia University, Darley developed and conducted experiments to explore the bystander effect and understand the circumstances that create it.
From the mid 1970’s to the mid 1980’s Darley turned his attention to pioneering efforts aimed at applying psychology to engineering and energy conservation. He worked with colleagues on how behavioral ideas can be used in energy conservation to better the environment and economy.
At the end of his career, Darley’s focus changed to the average person’s conceptions of law and the legal system. This interest of his turned into his main line of research. Darley saw the current reformatory strategy used in prison system as a poor one, he wanted to develop a psychology based reform strategy.