One legendary example is the case of Kitty Genovese, who was stabbed to death in 1964 by a serial rapist and murderer. The killing took place over the course of half an hour: the murderer initially fled the scene, scared off by a neighbor, but returned ten minutes later after realizing that no bystanders had interceded on Genovese's behalf. Exaggerated newspaper reporting following Genovese's death claimed 38 witnesses watched the stabbings and failed to intervene. Although in reality the police were alerted on both attacks and only one of the total of a dozen witnesses observed that there was a stabbing going on, the phenomenon is still referred to as the Genovese syndrome or Genovese effect. A September 2007 article that reviewed coverage of the Kitty Genovese murder in social psychology textbooks concluded the story of 38 witnesses is like a parable.
In 1972, Dr. Wolfgang Friedmann, professor of law at Columbia University, was murdered in broad daylight and bled to death on the sidewalk. The death of Deletha Word near Detroit in 1995 after witnesses failed to thwart her attackers, as well as the James Bulger murder case, are often cited as other highly publicized cases of the effect.
A 1968 study by John Darley, now a professor at Princeton University's Department of Psychology, and Bibb Latane first demonstrated the bystander effect in the laboratory. They ran some simple studies such as the following: A participant is placed alone in a room and is told he can communicate with other participants through an intercom. In reality, he is just listening to an audio recording and is told his microphone will be off until it is his turn to speak. During the recording, one participant suddenly pretends he is having a seizure. The study found that how long the participant waits before alerting the experimenter varies directly with the perceived number of other participants. In some cases, the participant never told the experimenter.
A common explanation of this phenomenon is that, with others present, observers all assume that someone else is going to intervene and so they each individually refrain from doing so and feel less responsible. This is an example of how diffusion of responsibility leads to social loafing. People may also assume that other bystanders may be more qualified to help, such as being a doctor or police officer, and their intervention would thus be unneeded. People may also fear losing face in front of the other bystanders, being superseded by a superior helper, offering unwanted assistance, or the legal consequences of offering inferior and possibly dangerous assistance. Another explanation is that bystanders monitor the reactions of other people in an emergency situation to see if others think that it is necessary to intervene. Since others are doing exactly the same, everyone concludes from the inaction of others that other people do not think that help is needed. This is an example of pluralistic ignorance and social proof. An alternative to explanations of rational motivation is that emotional cues to action can be as powerful as irrational ones, and the presence of a group of inactive others is a pre-rational emotional cue to inaction that must be overcome.
To counter the bystander effect when one is the victim, a studied recommendation is that one should pick a specific person in the crowd to appeal to for help rather than appealing to the larger group generally. Pointing directly to a specific bystander, saying their name if known, and giving them a specific task such as "You. [Or name.] Call the police." place all responsibility on a specific person instead of allowing it to diffuse. Furthermore, pluralistic ignorance is countered by the implication that all bystanders are indeed interested in helping, and social proof kicks in when one or more of the crowd steps in to assist.
In more modern situations in the United States, the fear of a liability lawsuit may factor into the bystander effect. With lawsuits so prominent in modern U.S. society, a person who may have helped a victim may not, under fear of making the situation worse and consequently being sued.