Shanghai prosecutors have approved the formal arrest of Yang Jia - the Beijing man they say killed six officers and wounded four people in an assault on a police station last week - on murder charges. Xinhua quoted an official from the Shanghai Municipal Procuratorate that the suspect had 'meticulously' planned the bloodbath, with 'grisly measures' that resulted in 'extremely serious consequences'. In the most detailed account yet of the incident, police yesterday defended their previous detention of Yang on suspicion of stealing a bicycle, which he claimed was his motive for the attack. Yang had 'candidly confessed', a police statement said, and it quoted him as saying he 'wanted this matter to have a bigger impact on society'. A police officer detained Yang on October 5 after he was found to be riding a bike without a licence plate. He refused to show identification or proof of where the bike came from, resulting in his detention. He was abusive and unco-operative at the station, the statement said. Police rejected an internet posting saying Yang was beaten in detention and said the person who spread the rumour, identified as Suzhou man Jia Xiaoyin, had been arrested for publishing false information, local media said. Still, Yang sent several e-mails complaining about his treatment, calling for the resignation of the officers involved and requesting compensation. A police supervisory branch dismissed his claims. The police statement said Yang was mentally capable of taking responsibility for the attack, and his lawyer, Xie Youming , told China News Service that his client's mental state appeared normal. Though the claim still has to be certified by a court, it makes it less likely that Yang will plead insanity in his defence. Yang carried petrol bombs, a knife, tear gas and other equipment. He carried out surveillance from a hotel near the station for several days.