Story highlights Rights Group: Author, filmmaker and activist Du Bin has been detained by police in China

Du was last seen in May, the same month he released a documentary on a China labor camp

Family members found two copies of a police subpoena at Du's residence in Beijing

A Chinese journalist, whose work exposed alleged human rights abuses of the government, has been detained by secret police in Beijing, said a close friend and human rights groups.

Du Bin released a feature-length documentary on the notorious Masanjia labor camp in May. He vanished later that month, says Hu Jia, an activist and friend of Du.

Hu says the last time Du's friends heard from him was 10 p.m. on May 31. Friends went to his apartment to look for him the next day but no one answered the door.

Hu says family members found two copies of an unsigned police subpoena at Du's residence in Beijing.

Copies of the alleged warrants viewed by CNN suggest that Du faces allegations including disturbing public order.

Hu says they have heard from two separate eyewitnesses that Du was taken into detention by force. "We confirmed that Du Bin was taken by 10 secret police. Two in uniform and the rest in plain clothes," says Hu.

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"Du Bin is a very respected professional photographer, documentary film-maker and author with a distinguished record of collaboration with international media organizations," says Nicholas Bequelin, a senior researcher at Human Rights Watch.

Du recently released a book on the Tiananmen massacre that was published in Hong Kong.

His documentary on Masanjia focused on interviews with former inmates of the labor camp.

China maintains an extensive network of labor camps across the country used to punish petty criminals like prostitutes and thieves.

But activists say they are used by the government to detain political activists and members of the outlawed religious group Falun Gong.

Hu said that most of Du's belongings had been taken from his residence including his laptops, copies of his books, and hardware used to edit his documentary.

CNN sought comment on Du's whereabouts from the Ministry of Public Security, which did not respond to our requests.

"Du Bin's detention on criminal charges is a worrying signal about the attitude of the new leadership towards dissent. The charges against him are unfounded and a transparent strategy for the authorities to silence him and intimidate others," says Bequelin.

"We believe that he is at risk of torture."