Conversation so far:
when was Chen Guangcheng detained?
On 7 September 2005, while Chen Guangcheng was in Beijing, he was reportedly abducted by security agents from Linyi and held for 38 hours.
why was  Chen Guangcheng detained?
Chen Guangcheng said that authorities threatened to levy criminal charges against him for providing state secrets or intelligence to foreign organizations.

Question: when did his trial started
Self-contained rewrite: when did Chen Guangcheng's trial start?