Members of the Richmond, Calif., community were stunned by the alleged rape and assault of a high school student after a school dance last Saturday.
But a nationwide news audience was even more astonished by allegations that about 20 people in the immediate area observed about 10 men and boys gang rape and beat the 15-year-old girl for two-and-a-half hours on the Richmond High School campus and did not contact authorities.
Psychology experts say the incident, if it occurred as described, may have been the result of escalating wildness facilitated by an isolated, heavily male environment.
"If one of the boys or men grabbed her and pulled her toward him ... and somebody else did something else so it became more and more sexual in nature ... we now have a [group of boys] who are pretty wild," said John Darley, a professor of psychology and public affairs at Princeton University. "Each act licensed what had gone before, and it also made more likely what came next."
Anyone who had reservations about the unfolding events "was surrounded by people who were apparently tolerating what was going on and maybe even encouraging it," Darley said.
In fact, several of the onlookers cheered and made comments as the student was assaulted.
"There was a group that was OK with it and observing, and then people that were sending messages and talking about it and treating it as if it were something to be viewed, like an exhibit," Richmond Police Lt. Mark Gagan told ABC News. "I really wish there was a way we could hold people accountable for what I think is an atrocious behavior."
Five people, ranging in age from 15 to 19, have been arrested in connection with the attack and appeared in court Thursday. Only the youngest, also a student at the school, entered a plea: not guilty.
Though refraining from participating in such an incident could indicate ambivalence, Darley said that, remaining present could be interpreted as implicit acceptance.
In such company, those who are uncomfortable may feel they risk ridicule and even personal injury by speaking out or leaving or calling the police.
Meg Bossong, coordinator of Community Education and Outreach at the Boston Area Rape Crisis Center, said the case suggested elements of the bystander effect, in which people are less likely to respond to an emergency when there are others around.
"That idea [is] that the more people there are around, the fewer people will get involved because there's a diffusion of responsibility," she said. "Not stepping in sends the message that it's not such a big deal. ... This is something that we hear a lot about around crime and also around sexual assault."
The element of sexual violence in the alleged attack at Richmond High School may have contributed to observers' apparent inaction.
"Because the weapon in sexual assault is a sex act, people see that as private," Bassong said, even though such violence is a community issue. "There's a complexity to it that may not exist if the weapon was not sexual."
The problem can be exacerbated, she added, by confusing messages from movies, television and pornography, which can portray relationships involving power and dominance as acceptable, healthy sexual behavior.