But Liu and the dozen officers who crowded into his dark Beijing apartment knew the reason. He was hours from releasing Charter 08, the China democracy movement’s most comprehensive call yet for peaceful reform. The document would be viewed by the ruling Communist Party as a direct challenge to its 60-year monopoly on political power.

Liu, who over the past two decades had endured stints in prison and re-education camp, looked at the blank detention notice and lost his temper.

"At that moment, I knew the day I was expecting had finally come," his wife, Liu Xia, said recently as she recounted the night of Dec. 8, 2008. Thinking of the Beijing winter, she said she brought him a down coat and cigarettes. The police took the cigarettes away.

Liu was sentenced last Christmas Day to 11 years in prison for subversion. The 54-year old literary critic is now a favorite to win the Nobel Peace Prize — in what would be a major embarrassment to the Chinese government.

He is the best shot the country’s dissident movement has had in winning the prestigious award since it began pushing for democratic change after China’s authoritarian leaders launched economic, but not political, reforms three decades ago.

Last year the prize was won by President Barack Obama. Other contenders for this year’s prize include Zimbabwe Prime Minister Morgan Tsvangirai.

In an indication of Beijing’s unease, China’s deputy foreign minister has warned the Nobel Institute not to give the prize to a Chinese dissident, the director of the Norway-based institute said this week. In another sign of official disapproval, an editorial on Thursday in the state-run Global Times newspaper called Liu a radical and separatist.

In China, police continue to threaten and question some of the more than 300 people who were the first to sign Charter 08, which was co-authored by Liu. Despite the risk, thousands more have signed it since its release.

Charter 08 is an echo of Charter 77, the famous call for human rights in then-Czechoslovakia that led to the 1989 Velvet Revolution that swept away the communist regime. The charter for China calls for more freedoms and an end to the Communist Party’s political dominance. "The democratization of Chinese politics can be put off no longer," it says.

Former peace prize winners Archbishop Desmond Tutu, the Tibetan spiritual leader the Dalai Lama and Charter 77 co-drafter Vaclav Havel have joined those calling for Liu to get the award. Scholars inside and outside China have mounted letter-writing campaigns on his behalf.

"If I were the Chinese Communist Party, I would free him now. Release him. Now. So you don’t have the humiliation and it’s good for everyone," said Jean-Philippe Beja, a China scholar at the Paris-based Center for International Studies and Research and a longtime friend of Liu.

The blunt, sometimes earthy Liu is not always liked, even by fellow activists. "He hasn’t yet become the kind of inspiring person Mandela is," AIDS activist Wan Yanhai said in a Twitter post this week, referring to the former South African leader, also a Nobel laureate.

But Liu is rare among government critics in China for being well-known not just among the dissident movement but among the wider public too.

"Across the spectrum, Chinese intellectuals and students have high respect for Liu Xiaobo," said Andrew Nathan, a professor at Columbia University in New York who once sponsored Liu as a visiting scholar. "The award of the prize … would be viewed by most as an act friendly to China."

It was not the same when the Tibet-born Dalai Lama was awarded the peace prize in 1989. Not just the Chinese government but some of the public too were angry over the win by the exiled Buddhist leader — regarded as a traitor by officialdom for his views on Tibet’s status.

Liu first drew attention in 1986, when he criticized Chinese writers’ "childish" obsession with the Nobel Prize. Two years later, he became a visiting scholar in Oslo, where the peace prize is awarded.

There, in his first time outside China, his writings became more political.

"Perhaps my personality means that I’ll crash into brick walls wherever I go," Liu wrote from Oslo to Geremie Barme, a China scholar at Australian National University. "I can accept it all, even if in the end I crack my skull open."

Liu cut short a visiting scholar stint at Columbia University months later to join the Tiananmen Square protests in Beijing in 1989. He and three other older activists famously persuaded students to peacefully leave the square hours before the deadly June 4 crackdown.

"I remember clearly the difficulty and pain Liu Xiaobo and his comrades-in-arms — raised as they had been with the most radical type of an education — experienced in reaching this decision, one which only later was understood to have saved the lives of several hundred students," Xu Youyu, a professor with the Chinese Academy of Social Sciences, recently wrote in a public letter supporting Liu for the peace prize.

Liu went to prison after the crackdown and was released in early 1991 because he had repented and "performed major meritorious services," state media said at the time, without elaborating.

The bloody Tiananmen experience made Liu less radical, said Zhou Duo, a friend on the square.

"He used to be impetuous, but he changed a lot after June 4," Zhou said. "He became more rational and mild. He criticized the Communist Party, but he preferred having good exchanges between government and the opposition about politics and democracy."

Still, five years later Liu was sent to a re-education camp for three years for co-writing an open letter that demanded the impeachment of then-President Jiang Zemin.

Liu emerged from that sentence in 1999 to find the Internet age. He resisted the new medium of communication at first, but eventually called the Internet "God’s present to China."

Now Liu only writes a diary and letters to his wife, which she keeps private. His family can visit him in prison, but they can’t talk about his case or world events, and officials stand by taking notes.

His wife said the couple had never imagined Liu winning the peace prize.

"I can always predict when bad things are about to happen," she said, "but I can never totally believe that good things can become a reality."

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Associated Press Writer Isolda Morillo contributed to this report.