What makes a crowd of adults watch passively as a young girl is raped, while in another case, a 14-year-old boy, armed only with a stick, confronts a grown man to save another little girl?
"The research shows that bystanders tend to try to interpret what they are seeing so it does not make it look, or be, horrible," said Mike Stein, with NOVA, a victims' rights group based in Washington. "They use a filter to interpret what is going on. A person who is acting hysterically is a drunk, for example.
"The more people there are observing something, the less likely that someone will act," said Stein. "They get their cues from someone else. If you get just one person to do the rescuing, the rest will join in."
Studies show that witnesses tend to pass on the responsibility, telling themselves that someone else will make the call.
A 1968 study by Bibb Latane and John Darley proved that point. By 1981, 56 more experiments confirmed the results and expanded on them.