The case concerns police in Kunming, who, in March, were patrolling an area known for vice when they detained two girls outside their home on suspicion of prostitution, then detained their parents and two friends when they went to see what was happening. The six were released the next day due to lack of evidence, but were taken back into police custody last month.

'Butcher' claimed to have found witnesses who could testify that the six were beaten after being taken away the second time, and tracked the elder daughter to a place where she was being held under 'house arrest', supposedly after being interrogated for a week.

At one point, his postings attracted thousands of responses from supporters and detractors. The latter criticised him for being too aggressive and rude in his dealings with officials; for the way he used donations from netizens to cover his expenses and to support Deng's family; and for enjoying the spotlight too much.

'I am just an ordinary citizen, a volunteer, a netizen, who helps those whose rights have been infringed,' Wu Gan, the man behind the 'Butcher' alias, told the South China Morning Post. He said he was spurred into action in Deng's case because he wanted to create a better society for his teenage daughter.

'I follow my conscience, and I am not afraid of criticism,' he said. 'The question we should ask is: why am I attracting so much criticism when I'm not breaking the law?'

Mr Wu said the situation in Yunnan was much more complicated than that of Deng, who was investigated for murder but was convicted three weeks ago of intentionally causing bodily harm and set free. Many of Mr Wu's supporters are convinced the Kunming police and propaganda department were behind criticism in internet forums. Mr Wu used his blog to reveal he has filed complaints against the police and Kunming prosecutors.

The emotionally charged criticism aside, questions are being raised about whether a court can admit evidence he has collected, and how far a netizen without legal powers to investigate can go. Still, experts and activists have welcomed his work and think there will be more investigative netizens.

'Without him, this Kunming case would have faded from public attention,' said Chang Boyang , a lawyer in Henan who ultimately became the family's lawyer because of Mr Wu's efforts.

'He played a very critical role in keeping it alive. As an ordinary citizen, he has more freedom in the way he handles matters, and he receives no pressure from any institutions. He answers only to the netizens, and this is a good thing.'

Internet expert Isaac Mao said 'Butcher' should not be considered a 'citizen journalist' in the traditional sense, but more as an activist. 'However, his existence might help bring about a more open media environment,' he said.

Veteran rights activist Wan Yanhai compared 'Butcher' to a modern-day da xia - a heroic figure who is driven to help the weak through a natural sense of justice - but said there was room for traditional activists and this new force of netizen activists to learn from each other.

'For example, traditional activists can learn to rely more on the internet,' Mr Wan said. 'But we are also cautious about what justice-driven netizens can do. They are often less sensitive to the intricacies of a situation.'

The crime of prostitution had a lot of grey areas and it was possible the police allegation was justified, he said. The family involved also had a history that angry police officers could easily use against them.

'In such complicated cases, direct confrontation may not be the best approach,' he said.

Intriguingly, Wu Hao, deputy director of the Yunnan propaganda department, has used the internet ID 'Truth-seeking force' to post responses in Web forums this week, saying he must clarify some misrepresentations by 'Butcher'.