Every year in Japan, some 1,800 men are arrested for groping women on trains. In a 2004 NHK survey of Tokyo women in their 20s and 30s, 64 percent said they had been groped on a train. Only 2 percent reported it to police. In 2008, the police in Tokyo, Kanagawa, Chiba and Saitama recognized 2,416 cases of groping on a train.

In a stepped-up campaign of intervention, police are apprehending suspects and putting pressure on operators of the growing number of "how to" Web sites for gropers (chikan). These sites offer advice on techniques for groping and escaping as well as online chat rooms where potential gropers can conspire to commit crimes, increasingly in organized groups.

Groping is a crime rooted in distorted psycho-sexual attitudes. For many gropers, the thrill comes from the power to frighten women, just as with bullying, another national problem. Its larger social context stems from a psychological fear of intimacy and a breakdown in relations between men and women. But what might have drawn just a snicker from some people decades ago is now more accurately understood as a serious form of sexual assault.

Solutions are mixed. The development of police forensics makes it possible now to obtain physical evidence of rubbing, touching or chewing on hair, a common act. Security cameras in train cars do offer limited results in overcrowded conditions. Broader awareness from signs and announcements and the protection afforded in women-only cars also are of some help. It's more important that women feel unafraid to speak out and that people around them be willing to help when they do.

Caution is needed, however, to avoid false accusations, like the one that resulted in the Supreme Court's overturning the conviction of a professor in April.

Freedom of speech, too, must be respected, even when it is offensive. The line between reading a Web site and committing a crime is wide for most people. Punishment should be appropriate and accompanied by rehabilitation or community service.

The silence on this issue must end. Gropers have counted on the silence of women — and, indeed, anyone — to get away with their crime.