Ai Weiwei cousin freed but others from his circle still missing

Police have freed Ai Weiwei's cousin after granting the artist bail himself.

Ai was released on bail on Wednesday night after 81 days of detention "because of his good attitude in confessing his crimes" and a chronic illness, the Xinhua news agency reported.

The 54-year-old told the Guardian he was happy to be back with his family but was unable to comment further. He appeared tired and thinner than before his disappearance.

Ai's mother, Gao Ying, said her nephew Zhang Jinsong, who had worked for as the artist's driver, returned home in a good mental state but had lost around 9kg (20lb). Zhang went missing a few days after his cousin.

"They have returned home and the family can see each other. We are all very happy. For anything that happens there must be an ending, and now we are happy with the result of what has happened to us," said Gao.

Earlier she said she was delighted that Zhang was to be released "since he got into the case because of my son". The 43-year-old cousin, known to friends as Xiao Pang, travelled and worked closely with Ai.

Three other associates who went missing shortly after Ai remain unaccounted for.

The Xinhua report on Ai's release cited police claims that a company controlled by the artist had evaded a huge amount of tax and intentionally destroyed accounting documents. It said the decision to grant bail reflected the fact he had repeatedly said he was willing to pay the taxes.

But Ai's family believe the accusations are retaliation for his social and political activism and that those connected to him – friends and colleagues – have been drawn in.

They include Ai's friend Wen Tao, 38. Wen's girlfriend, Shi Jing, said his family had received no information about him.

"I am always worried about Wen Tao and concerned that he might be persecuted inside there," said his friend Wu Yuren, an artist who was tried but never sentenced for assaulting a police officer in what he said was retaliation for his activism.

In his first public comments since his release on bail in April, Wu said: "I am concerned about the direction this country is going towards. Especially for intellectuals and artists, we are all concerned. There is less and less free space."

Hu Mingfen, 55, the accountant for the company that handled Ai's affairs, and Liu Zhenggang, 49, a designer who worked at the artist's studio, are also still missing.

Asked whether police were holding the trio, and if so why, a foreign ministry spokesman, Hong Lei said: "China is a country under the rule of law. For the specific situation please consult the competent authorities."

Police have refused to answer questions about them or register them as missing.

Hong told a news briefing that Ai was "not allowed to leave the place he was living in" without permission, but did not clarify whether that meant his home or Beijing as a whole. Bail restrictions usually prevent a suspect travelling without prior approval.

The spokesman confirmed that bail conditions would last for a year but declined to give further details of Ai's situation, such as restrictions on his speech or whether he was allowed to make or exhibit art.

Hong denied that China had bowed to international pressure, telling reporters: "The handling of Ai Weiwei's case was the handling of a very common economic crime.

"China is a country under the rule of law. We hope countries respect its judicial sovereignty without interfering."

He said Ai had been under residential surveillance from the day he vanished, 3 April. The measure does not require police to notify families – as detention would – and gives police six months rather than one before they have to refer the case to prosecutors. It usually equates to house arrest but the regulations do not spell out what constitutes a residence. Ai was held at an unknown location.

Human rights groups have warned that in recent months dissidents and activists have been coming under intense pressure even after release from jail or detention. Some have effectively been held incommunicado.

Zeng Jinyan, the wife of the jailed activist Hu Jia, is understood to have left their young daughter with relatives after police warned that his release from prison on Monday could mean tight restrictions on their movements, probably amounting to house arrest.

"Baobao cried her heart out on 19 June when I left for airport," Zeng wrote in messages on a Chinese microblog service. "She asked if I could work from home and stay with her ... I embraced Baobao for such a long time before saying goodbye to her that I can still feel her in my arms now."