Unless we ramp up the pressure on people to report crime, we risk ceding our communities to the power of thugs, rapists, and “no-snitch” bullies.

In Northern California, four young men, ages 15 to 19, have been charged with rape and special circumstances that could put them behind bars for life for the alleged gang assault of a 15-year-old girl outside a high school. But what of the nearly two-dozen people, including adults, who watched the alleged gang rape last Saturday and did nothing?

This wasn’t just a few people standing around watching a barroom brawl or consensual group sex. This was a group of folks finding entertainment value in human savagery.

Cops say more arrests are likely for some of the witnesses—for “aiding and abetting”—but only if they can prove some degree of active participation that somehow facilitated the crime. Those who only enjoyed the spectacle will face no charges, though nearby security guards who also reportedly did nothing can and should face civil lawsuits for negligence.

• Amy Siskind: It Could Have Been Your DaughterThis is when I start to think we should stop claiming to be the most civilized nation on earth.

If two-dozen people can stand by and do nothing while a group of men forces a parade of penises and other objects inside a defenseless 15-year-old girl, there’s a long list of words and phrases I can think of using—but civilized isn’t among them.

Yet we have no laws in place to punish or deter such vicious passivity.

Oxymoronic as it might sound, “vicious passivity” is exactly what we’re talking about. This wasn’t just a few people standing around watching a barroom brawl or consensual group sex.

This was a group of folks finding entertainment value in human savagery.

Four animals (apologies to PETA activists for the insult) allegedly did things to a teenage girl that even the most hardened criminals don’t do to each other behind bars. And while it’s incomprehensible that not one of them had the capacity for a moment of decency, it’s almost harder to understand how two-dozen people thought so little of the crime that not one of them did anything to help.

If this case is an expression of how some young men feel about sexuality and violence, it simply isn’t practical anymore to expect people to treat each other with civility. And even if this case is an anomaly, one 15-year-old suffering the way this victim did is more than any society should tolerate.

That so many people watched and did nothing suggests that we not only need tougher enforcement of laws against sexual violence—only a small percentage of rapists spend even one day behind bars—we need better ways of incentivizing bystanders to give a damn. Put another way, it’s embarrassing that doing nothing is OK, but without some legal ramification for such interpersonal inertia, doing nothing will always be the preferred path of least resistance for many people.

One case doesn’t an epidemic make, but gang rape isn’t exactly rare. It happens often enough that there’s actually a pet name for it. “Running a Train” is what opportunistic rapists call it when they line up to get “f—ked,” as one person reportedly described it to a bystander outside Richmond High. In short, it’s about guys reveling in the fact that there’s an incapacitated female body nearby to which a sex offender can do whatever he wants.

That one human being has the capacity to so mistreat another is not news. Nor is it shocking that laws against sexual violence have failed to prevent rape. Rapists don’t respect women—why would they respect the law? But there’s a good argument that requiring witnesses to report sexual violence to police when they see it might actually make a difference in reducing incidence rates.

It’s hard to know what the impact of such a law might be because in the few states that have such laws, such as Massachusetts, the crime of failing to report a crime is almost never enforced, partly because it’s a tough crime to uncover, but also because civil libertarians complain that it offends individual liberty to require people to do anything to further the efforts of law enforcement.

Naysayers also will complain that we can’t expect people to “snitch” on each other because the risk of retaliation is too great, and because they have to remain silent in order to survive in their communities. One study found that the Los Angeles County district attorney investigated 1,600 cases of witness intimidation, a number that has grown consistently in recent years. In more than 1,000 gang-violence cases, witnesses refused to cooperate.

But citizens have a right and a duty to testify in judicial proceedings. If a person is summoned to appear in court and doesn’t show up, he or she can be arrested and sent to jail. The system itself, not the police and prosecutors, has a right to insist on “everyman’s evidence.” It isn’t fascism, it’s democracy in action.

It would be even better if we could encourage more direct bystander intervention, and not just criminalize the nonreporting of crime. But it’s a lot to ask folks to put themselves in harm’s way for the protection of others and the good of society—even though we expect firefighters, cops, and people in the military to do it every day for little compensation.

And there’s always a risk that encouraging witnesses to get personally involved in crime prevention will breed vigilantism. But most data from Crime Stopper types of organizations and neighborhood watch programs suggest the opposite is true. More involvement by citizens tends to increase the social stigma associated with unlawful behavior—which helps reduce crime.

I’m not saying we should all take CSI training and start snooping on each other about every suspicious thing we see and hear. But we know that mandatory child-abuse reporting laws help to protect kids by obligating nonoffending adults to file a report with protective-services agencies when there are “reasonable grounds” to believe that a child is being neglected or abused. If we can make a phone call when we think a child is in danger, is it too much to ask that we do the same thing when we know firsthand that a human being of any age is being brutalized?

Wendy Murphy is a former child abuse and sex crimes prosecutor who teaches at New England Law/Boston. Wendy specializes in the representation of crime victims, women and children. Her expose of the American legal system, And Justice For Some, came out in 2007. A former NFL cheerleader and visiting scholar at Harvard Law School, Wendy lives outside Boston with her husband and five children.