Police had to release a man who several metro passengers saw groping a woman on a Line 1 train during morning rush hour last Thursday.

The witnesses did what they were supposed to do and called the police, who were waiting on the platform at Xinzha Road Station for the accused groper, local media reported. His victim, however, refused to get off the train and speak with police. Without a formal complaint, the responding officers had no choice but to let the man go.   

Groping strangers is a crime in China. The charge, called molestation, carries a punishment of five to 10 days of administration detention.

The problem is widespread and widely acknowledged on the subway, yet few people are actually charged with the crime. Chinese media reported that 13 people were charged for groping someone on the subway in Shanghai in the first seven months of 2013. That's on a metro system that transports more than 6.86 million people a day on average, according to last year's figures.

Reports and videos of women being molested on the subway have shown that few victims call out for help.

Metro authorities have advised women who have been groped to immediately notify the authorities or call out for help. It's easier said than done.

There are some deep-seeded cultural values that make it difficult for women in China to report these crimes. 

First of all, calling out for help in this situation draws unwanted attention to one's body. It's not something most people relish doing, especially after a traumatic experience like getting groped in public. Even a simple statement like "he touched my butt" requires a woman to talk about her posterior in front of a train car full of strangers. It adds to the embarrassment of an already humiliating experience.

Although it might sound strange to Westerners, confronting subway gropers, even just by calling for help, could be considered immodest in China, though in a perverse way. In a country that reveres modesty, some people might see an accusation of sexual harassment as a form of bragging.

I doubt that most people would see it that way, but the situation might cause a woman to think twice about announcing that some stranger just puts his hands all over her.

In addition, any talk about sex remains a taboo for many women in China. Most of the women born before 1980 grew up in an environment that frowns upon discussing sex and sex-related topics. Although this taboo is weakening, it still might leave some women too embarrassed to publicly accuse a stranger of sexual harassment.

The authorities haven't shown much sensitivity to the problem. In one ham-fisted attempt at a public service announcement two years ago, the metro operator posted on its microblog a photo of a passenger wearing a dress so sheer you could see every detail of her underwear. The photo was accompanied by a comment that suggested the woman might be asking to be harassed. The poster then advised female passengers to dress more appropriately.

The post, which was widely criticized online, shows at the very least that the metro operator needed a lesson in gender sensitivity.

If authorities truly want victims to report incidents of groping and other sexual harassment on the subway, they need to make women feel more secure about speaking out.

The metro police could dispatch female officers to deal with these reports because victims might feel less embarrassed talking about the incident with another woman.

The changes would make it easier for women to report such incidents. But it still wouldn't be easy. That would require a change to society's underlying values and taboos.