Avant-garde artist Wu Yuren will be retried on a charge of obstructing public service after his court case in Beijing was dismissed yesterday for lack of evidence. Wu - who is a signatory of Charter 08, a liberal manifesto calling for democratic changes on the mainland - was earlier accused of cursing, and assaulting and hurting an officer at a police station. He faces up to three years in jail if convicted of obstructing public service. The legal tussle arose when Wu accompanied a friend to discuss a dispute with a landlord on May 31 at a Chaoyang district police station. The friend, fellow artist Yang Licai , wanted to file a complaint against the management office of the 798 art district, and Wu went with him to lend moral support. Yang said he heard Wu scream from a separate interrogation room and assumed he was beaten up by the police. Wu was detained from that day on. The four-hour hearing yesterday took place at Wenyuhe Court outside Fifth Ring Road. About 50 people, including friends, neighbours and microblog supporters, showed up. A security cordon was put up and guarded by about 25 policemen. Yesterday marked the first time Wu's wife - Canadian citizen Karen Patterson - had seen her husband since his detention on May 31. 'Seeing him today assured me that he is OK,' she said. Patterson was surprised to be allowed in as Wu's lawyer, Li Fangping , had warned her the day before: 'Don't count on it.' She had applied to attend the trial a week before but had not received any news. A three-minute video clip was presented during the trial. Wu was allowed to give his side and to comment after each presentation. Yang said he had heard Wu scream loudly, as though in tremendous pain, from the room. He said Wu told him the next morning that the police had hurt his arms. Li said the video did not show any physical conflict between Wu and policemen. He said he suspected it had been edited three times. 'The court has agreed to get hold of the original video from the surveillance camera in the police station,' he said. 'So far it's not clear whether the video is available or not. We will wait.' Patterson said the three policemen involved denied the beating. They testified that Wu had tried to hit them, she said. 'The retrial is a good thing, as the evidence was not substantial and the lawyer called for the review of the original video,' she said. Li said violence was widely used in detention houses, and there were five deaths in 2008. 'That was why surveillance equipment was required to be installed in interrogation rooms, but ... there are areas the cameras are blind to, such as in Wu's case.' Patterson said she believed Wu's ordeal was revenge for his activism. He led a group of artists, including Ai Weiwei , in February to protest in Changan Avenue against the encroachment of a real estate developer. As the avenue runs past Tiananmen Square, it is an extremely sensitive area for protests. Police stopped the march after 500 metres. Patterson said the hearing was marked by frustration. 'It was very overwhelming ... All we can do is to see what happens.' A date for Wu's retrial was not released.