By Michael Bristow
BBC News, Beijing
The police say lawyer Gao Zhisheng has gone missing
Concern is mounting for a Chinese lawyer who is believed to be in detention but has not been seen for nearly a year.
Foreign governments have urged Chinese officials to reveal the whereabouts of well-known activist Gao Zhisheng.
Human rights groups say it is unusual that there has been no formal word on why Mr Gao was taken and what condition he is in.
Officials have so far given only cryptic hints as to where he is. A foreign ministry spokesman said he was "where he should be".
The lawyer has long been targeted by the government, which has previously stopped him working, put him on trial and kept him under surveillance.
Mr Gao disappeared some time in January last year, leading to immediate concern from human rights groups.
He appeared briefly at his family's home in Shaanxi province the following month but was accompanied by people believed to be security officials.
Mr Gao stayed only a short time before leaving and has not been seen since.
The lawyer did manage to telephone his elder brother, Gao Zhiyi, last summer to say he was all right but he added that he was not free and did not say where he was.
Since then, nothing has been heard of him.
"We don't have any clue about where he is. He's simply evaporated. As his friends, we are very worried about him," said fellow Beijing lawyer, Li Fangping.
Gao Zhisheng, a self-taught lawyer, has not always been at odds with the people who run China. He was once a member of the Chinese Communist Party.
In 2001 he was acclaimed as one of the 10 best lawyers in the country by a publication run by the Ministry of Justice.
But he ran into trouble when he started to defend some of China's most disadvantaged groups, such as supporters of the banned spiritual movement, Falun Gong.
Mr Gao's law practice was closed down in 2005. The government said one problem was that the lawyer had failed to tell officials of a change of address.
The following year he was given a suspended prison sentence for "inciting subversion".
After that, Mr Gao and his family - he is married with two children - were subjected to constant surveillance by the authorities. He was even detained again in September 2007.
He said he was tortured while in detention.
His captors beat him with electric batons, held lit cigarettes close to his eyes and subjected him to psychological abuse over more than 50 days, he said.
"Many horrendous evils were committed that were too shameful to be written down in the chronicles of the governments of the world," he said in an account of the event that emerged after his latest detention.
Mr Gao's wife and children escaped China last year and now live in the United States but the relatives still in China have made efforts to find out where he is.
His brother travelled to Beijing in December and tracked down a policeman who had been involved in the case.
"I asked the police where my brother was. They said they didn't know. They claimed he has been lost and missing since September," Gao Zhiyi told the BBC.
This comment has worried the family and friends of the missing man.
"It is impossible for someone to be missing under the tight control of the police," said Teng Biao, another friend of Gao Zhisheng.
"I imagine that either he is still under police control or something else may have happened."
Human rights criticism
Foreign governments have also kept up the pressure on China to reveal the whereabouts of a man who has become well-known abroad.
"The United States is deeply concerned about Gao Zhisheng's safety and well-being and we have raised our concerns repeatedly in Washington and Beijing," said a spokeswoman for the US embassy in the Chinese capital.
Journalists have raised the issue at the regular press briefings held by the foreign ministry - although the answers given to queries have failed to shed much light on the issue.
Foreign ministry spokesman Ma Zhaoxu initially said Mr Gao was where he should be. On Tuesday he said he did not know where he was.
All this is irregular, even in a country that often faces criticism for its human rights record.
Nicholas Bequelin, of Human Rights Watch (HRW), said families or work units should be notified if someone is detained.
He said those held by the Chinese state also had the right to receive letters and see a lawyer. But this had not happened in Mr Gao's case.
He added: "Generally when you have this kind of international exposure, the authorities tend to give the appearance of due process. But here that's not the case - there's something amiss."