Social psychologists Bibb Latané and John Darley popularized the concept of the bystander effect following the infamous murder of Kitty Genovese in New York City in 1964. The 28-year-old woman was stabbed to death outside her apartment; at the time, it was reported that dozens of neighbors failed to step in to assist or call the police.

Latané and Darley attributed the bystander effect to two factors: diffusion of responsibility and social influence. The perceived diffusion of responsibility means that the more onlookers there are, the less personal responsibility individuals will feel to take action. Social influence means that individuals monitor the behavior of those around them to determine how to act.