On the 19th anniversary of the June 4 crackdown on demonstrators in and around Tiananmen Square, human rights groups are highlighting the plight of the approximately 100 people they estimate to remain in jail in China for their activities in 1989. Stephanie Ho reports from Beijing.

Chinese police officers stand on guard after daily flag raising ceremony in Beijing's Tiananmen Square at dawn, 4 Jun 2008

The estimates of the number of Chinese people still in prison for their activities in 1989 range from 50 to 200.

John Kamm, whose San Francisco-based Dui Hua Foundation tracks political prisoners in China, says the list of so-called June 4 prisoners includes people all over the country.

"There's a fellow called Liu Zhihua, in Hunan," he said. "He's the last of a group of workers that organized one of the largest worker strikes in 1989, at the Xiangtan Electrical Machinery Factory. Leader Chen Gang, everyone else, has been released. He's still in. There's a peasant in Guizhou, by the name of Hu Xinghua, Miao nationality, set up something called the Chinese People's Solidarity Party. He's still in."

Kamm's organization and other human rights groups are calling on the Chinese government to release people put in jail for their 1989 activities, as a goodwill gesture before the Beijing Olympics in August.

"China, if you want to do something to improve your image, how about setting free the remaining June 4 prisoners, putting June 4 behind you?" he said.

Putting the events of 1989 behind her has not been possible for Ding Zilin, whose 17-year-old son Jiang Jielian was among the student demonstrators in Beijing's Tiananmen Square. He was shot and killed.

Ding Zilin, co-founder of the Tiananmen Mothers, stands in front of a shrine to her son, Jiang Jielian, at her apartment in Beijing, 4 Jun 2008

Ding heads a group called Tiananmen Mothers. Organization members send Chinese leaders an open letter on June 4, every year, demanding to know what happened to their children.

This year, she says the group has opened a website - tiananmenmothers-dot-org.

She says the website contains extensive and detailed evidence for 188 demonstrators who were killed around Tiananmen Square, when the army opened fire on student protesters.

The documentation includes two maps that pinpoint the location where each of the victims died.

Although the website is freely available outside China, Ding says Chinese authorities blocked it within the country after it was open for only three hours.

The Chinese government consistently has ignored Ding's appeals and has officially labeled the 1989 student-led movement a "counterrevolutionary rebellion."

Foreign Ministry spokesman Qin Gang reaffirmed this position in an answer to reporters in Beijing, Tuesday.

He says there is already a clear conclusion about the events around Tiananmen Square in 1989.

Undeterred, people like Ding Zilin continue to lobby for an answer. She misses her son and laments that nearly 20 years after the June 4 crackdown, a new generation of Chinese young people is growing up with no knowledge of what really happened.