Twenty years after Chinese troops brought the massive pro-democracy protests in Tiananmen Square to a bloody end, Beijing is in lockdown.

Active dissidents have been confined to their homes or forced to leave the city and their mobile phones have been shut down. Social networking and image-sharing websites such as Twitter and Flickr have been closed to prevent discussion of the anniversary. Near the square itself, workmen have been preparing Chang'an Avenue, the Avenue of Eternal Peace, for a huge parade to celebrate the 60th anniversary of the Communist Party's accession to power, but the 4 June massacre will be marked with tight-lipped silence and a steadfast official refusal to revisit the events of that day.

Twenty years ago Tiananmen Square was full of frantic students wearing headbands and lobbying for democratic change. Today it is full of tourists eager to get their photograph taken in front of the Forbidden City with its huge portrait of Chairman Mao Zedong. Shiny Mercedes and Buicks now swish along the road at the point on the avenue where a lone, unknown protester stood in front of the tanks with his shopping bags 20 years ago, and briefly halted the advance of the People's Liberation Army. The Communist Party has forbidden discussion of the events of that day 20 years ago, and the official line is that the crackdown, officially called "the political incident", was necessary to ensure stability. The student movement that drove the democracy activism in late 1980s China has largely evaporated, its leaders all in exile or no longer active.

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The high drama of Tiananmen Square's protests set in motion the chain of events which led to the fall of the Berlin Wall and the opening up of eastern Europe. But in China the revolution was stillborn. A year after the crackdown, Jiang Zemin, who was president at the time, dismissed international condemnation of the Tiananmen massacre as "much ado about nothing".

The massacre caused horror around the world, and China was marginalised by the international community, but as Deng Xiaoping reportedly said: "The West always forgets." The lure of China's huge potential market was too great for condemnation to last long, and China was soon back at the high table of the international community. Twelve years after the crackdown, China was a member of the World Trade Organisation and is now the world's third largest economy.

China is a very different place these days. The government has begun to implement some of the freedoms the protesters on the square had sought, such as getting rid of rules dictating where Chinese could live or work, and even the person they could marry.

The past two decades of astonishing economic advances have given millions of Chinese a say in their destinies. One of the students' key demands was for an end to the corruption that blighted daily life in China. The Chinese government is engaged in a highly public campaign to crack down on the corruption which it once denied existed, though in the absence of a free media or speech, critics say the campaign is doomed to fail. But some things have not changed. All power in China flows exclusively from the Communist Party and independent political activity is forbidden. Nearly all of China's active dissidents have been exiled or imprisoned.

The recent Charter 08 campaign, a petition calling for legal and political reform, was the closest thing to a pro-democracy movement that China has seen for years, and one of the chief architects of Charter 08 and one of China's best-known intellectual critics, Liu Xiaobo, has been detained. Mr Liu spent two years in prison for his role in supporting the Tiananmen students. He also prevented more bloodshed by successfully negotiating with the army the evacuation of the last remaining students on Tiananmen Square in the early morning of 4 June.

The text of Charter 08 included a direct reference to the events on 4 June, as an example of the "long trail of human rights disasters" caused by the Communist Party's monopoly on power, Human Rights Watch said. "Liu Xiaobo epitomises how the Chinese government has responded to Tiananmen in particular and peaceful critiques in general: by stifling them," said Sophie Richardson, Human Rights Watch's Asia advocacy director.

The San Francisco-based rights group Dui Hua estimates that 30 people remain in prison for offences related to the Tiananmen crackdown. The prisoners – then mostly young workers – were jailed for burning army trucks, stealing equipment or attacking soldiers as the military advanced toward the protesters.

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Cui Weiping, a professor at the Beijing Film Academy, recently called for open discussion of the events of that day. "What kind of negative impact has it had on our society for us to keep silent and to conceal the event for two decades? How has it harmed the spirit and morality of this nation?" she wrote in a paper."If the situation remains the same for another 10 years, 4 June will no longer be a crime that was committed by a small group of people, but one that we all participated in," she said.

Tiananmen memories: Stories from the square

Survivor's guilt of exiled student leader

Wu'er Kaixi was one of the most famous student leaders, and while on hunger strike and wearing a hospital gown, he met Li Peng, the premier who subsequently ordered the tanks into Tiananmen Square, in a live TV interview, during which he rebuked Li Peng in a remarkable show of defiance. He lives in exile in Taiwan, but yesterday tried to turn himself in to the Chinese authorities in Macau in the hope of seeing his parents again. "Every day for the past 20 years, I have to deal with several kinds of emotion. Guilt is definitely one very important sensation that I have to deal with every day, survivor's guilt, the guilt of the captain of the sinking ship, and then, of course, anger, homesickness. And I guess, the guilt part is going to last as long as I live.

"I was at one of the front lines, at Dongzhimen. People were stopping the soldiers, imploring them, don't kill your brothers. It's amazing how angry Chinese people were, very emotional, and the retaliation was irrational, unreal, the forces were disproportionate, but it didn't stop people from crying.

"In 1989 we were at no point trying to overthrow the Communist Party. The mass was very restrained, very rational, very well organised. There are criticisms that the students pushed the government too far, which led to the massacre. I strongly object to that. Blaming the students is like blaming the victim who is being shot for not dodging the bullets fast enough, before blaming those who pulled the trigger."

'The doctors let my son bleed to death'

Xu Jue is a researcher at the Chinese Academy of Geological Sciences. "On 21 May 1989, my son Wu Xiangdong went out with his girlfriend and never came home. We found a note saying he wanted to make a sacrifice for his country's democracy and freedom. We are really proud of him as he was prepared to sacrifice his love for his parents and girlfriend for our country. He had supported the students' movement for a while, so I knew he would take part in this. Then my husband and I went to look for him. The next time I saw my son was in the hospital. He had been shot at Muxidi in the city, around 11pm on 3 June. But he was not dead. He was taken to hospital, but the doctor told me he was forbidden to save my son's life.

For two hours they just let him bleed to death... It was terribly painful. Everything changed. I continuously had severe headaches, I nearly went mad. The brainwashing began. Some people began to inform on others. Beijing was under martial law. Every night soldiers knocked on people's doors. We did not dare to turn on the lights at night. Some people were taken by the army and beaten severely.

"I was terribly depressed but I had to hide my sorrow. I even tried to commit suicide. I put on white clothes and walked through the streets. There were few other people walking because of martial law. But I walked through the streets because the soldiers were there, and I wanted them to shoot me."

20 years of threats and harassment

Pu Ziqiang is now 44 and a lawyer in the city. "We students only wanted to reform the political system. We did not cause any riot, rebellion or violent disorder. I was a graduate student at China University of Political Science and Law and before that I was a middle school teacher for two years. I didn't hesitate to take part in this movement as I thought it was what I must and should do.

"The government did not list me as a wanted person so I just went back home and resumed my life. Because of what they have done, reform of the Chinese political system has stagnated for 20 years. In the past 20 years I have suffered threats and harassment by the police. Everything the police do to me is illegal. During those 20 years, I also have thought a lot. In my view, what we called democracy was kind of empty at that time. Democracy is specific and concrete. We did not have a clear target. It contained more emotion than reason. But the government did not treat us properly. It was a crime. Now my hope is that the government will carry out a thorough investigation of what happened on 4 June."

'So many died – but our dream lives on'

Wang Dan is an iconic student leader who was twice jailed in China and is still a figurehead for resistance. He now lives in exile between Los Angeles and Taiwan. "I wasn't on the square on that night, 3 June, I was in Beijing University, so I didn't witness what took place. The next day, 4 June, some people told me what happened and with some others we escaped to southern China. I stayed there for about one month, hiding in my friend's apartment, but then I thought that if I keep on hiding it's no different from jail. So I went back to Beijing and I was arrested the very next day, 2 July.

"We escaped to watch what would happen. We still had some hope. Maybe there's some positive change, like the political struggle, maybe the leaders will go in the other direction, but we were wrong. I was very young.

"I was released in 1993 and imprisoned again in 1995. Of course, I couldn't shut up. So many people died and the dream we had was still a dream, I thought it was still my responsibility to fight again. I didn't want to betray my ideals. And that's my belief, to push China to go in the direction of democracy and human rights."

"Beijing insisted no more than 250 died ... For many these claims are hard to believe"

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