On 7 September 2005, while Chen was in Beijing to publicize his class action lawsuit against the Linyi city family planning staff, he was reportedly abducted by security agents from Linyi and held for 38 hours. Recounting the incident to foreign journalists, Chen said that authorities threatened to levy criminal charges against him for providing state secrets or intelligence to foreign organizations. After Chen refused negotiations with local officials to cease his activism, Linyi authorities placed him under effective house arrest beginning in September 2005. When he attempted to escape in October, he was beaten.  Xinhua, the news agency of the Chinese government, stated that on 5 February 2006, Chen instigated others "to damage and smash cars belonging to the Shuanghou Police Station and the town government" as well as attack local government officials. Time reported that witnesses to Chen's protest disputed the government's version of events, and his lawyers argued that it was unlikely he could have committed the crimes due to his constant surveillance by police. Chen was removed from his house in March 2006 and was formally detained in June 2006 by Yinan county officials. He was scheduled to stand trial on 17 July 2006 on charges of destruction of property and assembling a crowd to disrupt traffic, but this was delayed at the request of the prosecution. According to Radio Free Asia and Chinese Human Rights Defenders, the prosecution delayed the trial because a crowd of Chen supporters gathered outside the courthouse. With only a few days' notice, authorities rescheduled Chen's trial for 18 August 2006.  On the eve of his trial, all three of his lawyers, including Xu Zhiyong of the Yitong Law Firm, were detained by Yinan police; two were released after being questioned. Neither Chen's lawyers nor his wife were allowed in the courtroom for the trial. Authorities appointed their own public defender for Chen just before the trial began. The trial lasted only two hours. On 24 August 2006, Chen was sentenced to four years and three months for "damaging property and organizing a mob to disturb traffic".  As a result of Chen's trial, British Foreign Secretary Margaret Beckett selected his case for the cover of the British government's 2006 human rights report, stating concern over the handling of Chen's case and calling for the Chinese government "to prove its commitment to building rule of law." A Globe and Mail columnist also criticized the verdict, writing that "Even assuming [Chen] did damage 'doors and windows,' as well as cars, and interrupt traffic for three hours, it is difficult to argue a four-year prison sentence is somehow proportionate to the offence."  On 30 November 2006, Yinan County court upheld Chen's sentence, and on 12 January 2007, the Linyi Intermediate Court in Shandong Province rejected his final appeal. The same court had overturned his original conviction in December 2006, citing lack of evidence. However, Chen was convicted in a second trial on identical charges and given an identical sentence by the Yinan court. Following the trial, Amnesty International declared him to be a prisoner of conscience, "jailed solely for his peaceful activities in defence of human rights".

Answer this question "why was he detained" by extracting the answer from the text above.
Chen said that authorities threatened to levy criminal charges against him for providing state secrets or intelligence to foreign organizations.