A state statute requires that people must report to police any information they have about the sexual assault of children under the age of 14. There is no law requiring people do the same for victims over that age.

"The fact that our victim missed that age by a very short time …" said Richmond Police Lt. Mark Gagan. "It's just very offensive that there's no statute we can use to show that we condemn their behavior."

Gagan said the assault began inside a homecoming dance Saturday night at Richmond High School. He said the girl was taken to a dark, remote corner on the campus and raped by as many as 10 males.

Gagan said Wednesday that police have arrested five males — between the ages of 15 and 21 — and charged them with a variety of felonies, including rape and kidnapping. He expected more arrests this week.

The attack put this industrial suburb of San Francisco in the national spotlight. Home to numerous refineries and loading docks, Richmond was ranked as the ninth most dangerous city in the USA in 2008, according to Morgan Quitno Press, a research company that tracks criminal data.

Gagan said up to 20 onlookers came and went but that no one called police until a woman overheard two witnesses talking about the attack and she reported it.

The case drew comparisons to other high-profile cases where groups of people fail to report heinous crimes, a phenomenon dubbed the "bystander effect." According to the theory, the likelihood that a witness reaches out for help decreases as the number of witnesses increase.

One notorious example of the phenomenon took place in Queens, N.Y., in 1964, when Kitty Genovese was attacked in the courtyard of an apartment complex. Numerous residents heard or saw portions of the attack and did nothing, though some details have been disputed. Studies have found that people in such situations either think someone else has called police, fear getting involved, or fail to help for other reasons.

David Hyman, a University of Illinois law professor who has studied the bystander effect, said the biggest misconception about such situations is that they happen often.

Hyman studied decades worth of data and found that no more than two people die each year because of a failure to attempt a rescue — either of a victim of a crime or of a natural occurrence, like drowning. By comparison, Americans perform over 1,000 "non-risky" and about 260 "risky" rescue attempts each year.

"We do have a problem: People too often get involved in circumstances that place the life of the rescuer at risk," he said.

However, in the Richmond case, Hyman said there was no doubt that someone should have called police immediately.

Eugene Volokh  a University of California-Los Angeles law professor, said the reaction to crimes involving disinterested bystanders is a call for a law requiring witnesses to report crimes.

He said those kinds of laws only exist in a handful of states and for good reason. In the case of the California law, the crime carries a maximum six months in prison.

Volokh said making the failure to report a crime a crime itself can seriously undermine the intent of the law. Many times people don't report a crime until some time has passed — maybe their guilt convinces them to call police, maybe they don't think a crime is occurring but later see a call from police for information. Those people may not come forward if doing so would be admitting to a crime.

"This makes it much less likely that they will testify later or that they'll talk to police later," Volokh found.

Peter Arenella, a UCLA law professor who studies the moral psychology of juveniles, believes the bystander effect should not even apply to the Richmond gang rape.

"In this context, when you're talking about a crime this horrific, and you're talking about a group of adolescents watching, there's much more serious pathology going on that can't be explained by, 'Someone else is going to call for help,' " Arenella said.