I happened to read this information and I copied it here FWIW.
In 1964, a woman named Kitty Genovese was beaten and killed in an attack witnessed by dozens of people, none of whom intervened. In studies to understand this phenomenon, psychologists discovered the “bystander effect” (sometimes called the “Genovese effect” after the victim), which says that the more bystanders witness an attack, the less likely it is that any individual will intervene. Each individual witness believes that someone else will intervene, and that their action is therefore not needed.
In a follow-up study to explore the effect of race in this equation, psychologists found that if a lone individual witnessed an attack by a white person on a black person, they were more likely to intervene than when they witnessed a white-on-white attack. When confronted with a racialized situation, most people feel compelled to intervene because not to intervene would make them feel like racists. In cases where other witnesses were present, the subjects were actually less likely to intervene in a white-on-black attack than similar subjects witnessing a white-on-white attack. In these instances, the presence of other potential interveners allows the subject to avoid the self-accusation of racism — they can tell themselves that they’re staying out of it because someone else will intervene, not because they’re racist.