Twenty years on from Tiananmen Square, John Garnaut argues there are glimpses of recognition of the sins of the past.

Few who were old enough to watch the news in 1989 will forget the television footage of the white-shirted man, shoulders slumped, briefcase in hand, staring down an advancing tank on Beijing's Chang An Avenue - the Avenue of Eternal Peace.

He became the global symbol of the Chinese protesters who bravely massed for seven weeks in Tiananmen Square to demand inclusive and clean government. But 20 years on, the world still does not know his name or whether he survived after slipping back into the crowd.

Nor do we know how many hundreds of students, workers and bystanders were ripped apart by bayonets and machine-gun fire, or smeared into the bitumen beneath the tank tracks on the approaches to the square late in the evening of June 3 and through Beijing's streets over the following days.

"Corpses littered Beijing's main boulevard, Chang An, with blood and torn limbs visible in several sections of the area outside the Forbidden City," reported the Herald's correspondent in Beijing, Peter Ellingsen. "One student as he lay dying scrawled in blood: 'Li Peng, you will never live in peace'."

But the outside world's fragmentary knowledge of the Tiananmen tragedy is vastly greater than what is generally known inside China. The Chinese Communist Party has controlled nothing so tightly as this black chapter in its history.

On the evening of June 3 - the eve of the massacre - loudspeakers in the square were embellishing the official record before the tanks even arrived: "A serious counter-revolutionary riot has broken out in Beijing. Thugs have stolen the army's ammunition and set fire to army trucks.

"Their aim is to destroy the People's Republic of China."

China was saturated in propaganda before the blood was dry. Mr White-shirt, they said, was a "lone scoundrel" whose asserted survival "proves that our soldiers exercised the highest degree of restraint".

On June 9 Deng Xiaoping called together his generals and signalled a massive rebuilding of party indoctrination in every institution: "In the last 10 years our biggest mistake was made in the field of education, primarily in ideological and political education."

The Communist Party rebuilt its propaganda apparatus, re-educated and re-vetted millions of officials and extended its reach into every realm of public communication. Loyalty to the party once again became the primary criterion for getting ahead.

The party did not spare its own. Zhao Ziyang, then Communist Party chief and architect of China's economic reforms, had broken the unwritten rule by refusing to sign up to the official story. He was accused of "splitting the party" and "supporting turmoil", and spent the rest of his life under house arrest until his death in 2005.

Officials soon found that voicing support for the crackdown was the fastest path to promotion. Parents learned to grieve in private for missing children. Traumatised students were force-fed a deluge of "patriotic education" - a project boosted yet again this year - after indoctrination lapsed in the more liberal mid-1980s. And those who could not be trusted to forget the Communist Party's blackest hour were imprisoned or banished overseas.

"I'm a dissident in exile," the Tiananmen student leader Wuer Kaixi says from Taiwan, where he manages an investment fund.

"I can't come back, I'm still on the most-wanted list."

Bullet holes along Chang An Avenue have long been covered over, paving stones mauled by tanks quickly replaced. The party has airbrushed all trace of the Tiananmen massacre from every public space. Internet screening has been redoubled as Thursday's anniversary draws near.

The party acts as if it would not survive even a gesture of public protest, let alone honest appraisal of how it gunned down its own at its most sacred place.

The strategy is working. "People don't really talk about June 4 any more," a confident public security official told the Herald. "We're far more worried about September, when university students graduate and find there aren't any jobs."

The party's obsession with manipulating its past makes the achievements of a few contrarian cadres all the more unlikely.

Du Daozheng joined the Communist Party in 1937, aged 14. He proudly rose through the ranks of a revolutionary party that fought back the Japanese, proclaimed the People's Republic and distributed land to peasants. He stuck with it as China took its Great Leap Forward, starving 30 million people to death, and as the Cultural Revolution killed countless others. Du was persecuted as a rightist when he ran a '50s regional office of the Xinhua news agency. Zhao Ziyang was the young deputy party secretary who stood by and let it happen; there are no untarnished heroes.

"I was quite blind in the past," says Du. "I have been persecuted by many, and I have persecuted many."

In the '80s, Du edited The People's Daily before heading the General Administration of Press and Publications. Then, on May 31, 1989, as tanks rumbled towards Beijing, Du says he shed many tears before phoning a senior leader and vowing to tear up his party membership card if soldiers opened fire.

But Du did not quit membership. He has spent 20 years chipping away from inside at the party's collective guilt, trying to clear the names of the reform-minded cadres it had destroyed. In the early '90s, Du and other liberals founded the magazine Yanhuang Chunqiu, which became China's only historically inquisitive political publication.

We visited Du late last year in his shambolic Beijing office after his magazine broke China's greatest media taboo by slipping into publication the name of the purged Zhao. From under his desk he pulled a book he had secretly published in Hong Kong.

It contains 700 mini-articles about the complex legacies of Tiananmen and has the banned date "June 4" on the cover. It reminisces about the party's fallen heroes, attacks the cancerous corruption and misrule guaranteed when officials are hired on ability to lie, and laments the party's inability to learn from the Cultural Revolution. The introduction reveals the articles were written for the Hong Kong press by Du and other senior cadres over the past 20 years, under the pen name Hai Ci. Countless Chinese have been jailed for doing much less. Some articles describe small details of Zhao's life under house arrest. It laments that in Beijing "if you supported the shooting you get promoted, regardless of performance".

The book no longer is secret. Nor is the introduction Du wrote for Zhao's extraordinary memoirs, published in English last week. The introduction details how Du persuaded Zhao of his duty to record his version of history. It says he and four other officials secretly recorded Zhao's testimony and smuggled it to Hong Kong for publication.

Du writes Zhao Zihang back into Communist Party history as a talented but not flawless man who became a hero for standing up for the truth: "At the critical historical moment of June 4 Zhao accepted his responsibility to the Chinese nation, history, and ordinary people. He set aside personal life and honour, took the side of truth and the people, and made no compromise, surrender, or concession. The fundamental cause of Zhao Ziyang's fall is that China lagged behind in political reform."

Zhao's invaluable memoirs make clear the Tiananmen protests were manipulated by ambitious hardliners, led by Li Peng, who sabotaged for personal gain opportunities for compromise. Ten times China's propaganda authorities tried to nobble Du's magazine and each time he has prevailed. On Saturday the magazine website was shut down but it was up again by lunchtime on Monday.

The server company was ticked off by a senior official and apologised to Du for its "mistake", even though the magazine carries an article penned by Chen Ziming, an exile who features on the Government's June 4 most-wanted list.

Du and his magazine are protected from on high. For the first time, the Communist Party has sanctioned a small but vibrant space where it can confront its turbulent past.

History also confronts the democracy leaders who occupied the square in 1989. Up close, they were also divided, confused and ill-equipped for real politics.

Hardliners on both sides rejected chances for compromise and thought their causes were helped by bloodshed. Said the most prominent democracy leader, Chai Ling: "Only when the square is awash with blood will the people of China open their eyes." He saw his duty as protest commander-in-chief to hold on to power "because I must resist compromise, resist these traitors".

Wuer, a moderate student leader who failed to convince peers to leave the square, says Chai has been unfairly criticised. "We were young; we were 20 years old at the time. It was stressful and emotional and I'm sure I said things that I would regret."

Wang Juntao was released from jail in 1994 and sent to the United States at the request of Bill Clinton. He now sees he overestimated the global democracy tide and underestimated the Communist Party's determination to cling to power. He argues the party gutted the country to restore itself.

"Corruption, inequality, injustice, collapse of morality and the social environment - those problems caused the '89 democracy movement but they are all much worse now," says Wang.

Many of the party's inside critics, including Du, would not disagree.

Zhao came to regret being too conservative when in power. He came to believe political reform was China's only way forward.

Wuer, the exiled activist, says each day he wakes to competing sensations of anger, survivor's guilt, hope and nostalgic yearning.

"Friends tell me it is no longer the same Beijing I miss," says Wuer.

History's verdict is far from settled. At least its writing has begun.

John Garnaut is the Herald's China correspondent.