The Modern Bystander Effect

Why don’t people intervene when they encounter violence streaming live online?

Social media promised to connect us with our friends, and the world beyond. We have discovered that that includes the happy, the sad and now, the depraved.

Perhaps it was inevitable that videos of playful cats would give way to the darker side of human nature, as ever-present cameras captured the violence taking place in society. But a new level of shock was reached recently when Facebook Live was used to show a live rape and a live beating.

The crimes were horrific enough, but other questions surfaced: Why would someone film an assault instead of intervening? And why didn’t those watching online call the police?

A phenomenon social scientists call the bystander effect was first identified some 50 years ago, after Kitty Genovese was killed outside her apartment in New York City. That case sheds light on behavior in the digital age.

View full episodes at

Related: What the Kitty Genovese Killing Can Teach Today’s Digital Bystanders by Clyde Haberman

Previous versions
At Retro Report, we update our journalism as news unfolds. Here are the previous published versions of this story.
For teachers
  • Producer: Catherine Olian
  • Producer: Karen M. Sughrue
  • Editor: Sandrine Isambert
  • Editor: David Feinberg
  • Associate Producer: Olivia Katrandjian

For Educators


This 11-minute video introduces students to the theory of the bystander effect, including a discussion of the killing in 1964 of Kitty Genovese that spurred John Darley and Bibb Latane to design research that validated the theory. The video shows students how the bystander effect can be used to explain and possibly prevent situations in which bystanders fail to report violence they have witnessed online. Useful for any lesson that introduces the bystander effect or explores the connections between social psychology and social media, the video also presents recently discovered facts that have called into question the established narrative around Ms. Genovese’s death.

Background reading

The failure of bystanders to report violence being livestreamed across social media is often blamed on the medium itself, but two social psychologists came up with a better explanation more than 50 years ago.

In the 1960s, John Darley and Bibb Latane were fascinated by the killing of Kitty Genovese in the Kew Gardens neighborhood of Queens. One night in March 1964, Ms. Genovese, 28, was sexually assaulted and stabbed to death while she was on her way home from work. There were reports that some 38 witnesses did nothing to stop the killing.

That, at least, was the front-page story in The New York Times two weeks after the crime. The apparent apathy and moral inaction of so many law-abiding citizens sent shock waves across the nation.

Darley and Latane wondered if there was more to the story. They conducted a series of experiments that led them to discover the bystander effect, the theory that the more witnesses to an event, the less likely it is that any one of them will intervene, in the expectation that someone else has already responded, or will.

Over the years, evidence has emerged that the Times story was innacurate. Two neighbors had, in fact, called the police. While dozens of people nearby heard Ms. Genovese’s screams, only a few saw the attack take place.

But the bystander effect has held up in other experiments and is still covered in textbooks, continuing to provide a critical insight into human behavior in the digital age.

Lesson Plan 1: Psychology: The Bystander Effect

Students will learn how social psychologists developed the concept of the bystander effect to explain passive reactions to a shocking crime in 1964, and how that theory can help to explain concerning behavior online today.

  • How the killing of Kitty Genovese in 1964 gave rise to the concept of the bystander effect, and how newly uncovered facts have called into question the original narrative that surrounded the case.
  • How social psychologists used experimental research to test the theory of the bystander effect.
  • How the bystander effect can be used to explain why viewers of violent online videos don’t report what they witness, and how knowledge of the bystander effect might be used to develop solutions to this problem.
Essential questions
  • How did the Kitty Genovese case inspire Darley and Latane to develop the theory of the bystander effect?
  • How did Darley and Latane design their experiment? What did it reveal?
  • What newly uncovered facts have challenged the established narrative surrounding the Kitty Genovese case?
  • How did Facebook respond to digital bystanders making and watching violent videos on its platform?
  • National Council for the Social Studies C3 Framework
    • D2.Psy.9.9-12.Describe how biological, psychological, and sociocultural factors influence behavior.
  • National Standards for High School Psychology Curricula
    • Sociocultural Context Domain: Content Standard 2: Social Influence2.2 Describe the effects of others’ presence on individuals’ behavior.
  • AP Psychology
    • Topic 9.I.1: Bystander EffectSkill 1.B: Explain behavior in authentic context.