Chinese artist and human rights activist Ai Weiwei says he was roughed up and detained by police last week when he and 11 others tried to attend the trial of an activist charged with subversion.

The accusations against Tan Zuoren are apparently tied to his investigation of the deaths of thousands of schoolchildren in last year's May 2008 earthquake, as well as essays he wrote about the 1989 student-led demonstrations in Tiananmen Square that ended in a deadly military crackdown. During last week’s trial, Tan tried to call three witnesses, including Ai, a high-profile government critic, but his requests were rejected. Ai says he tried to go to the court to support Tan, but four police officers carrying guns and batons barged into his hotel room at 3 a.m. to take him away. One of them struck him on the cheek when he questioned them, he says, while another supporter was also roughed up. Later that day, police released Ai and several others. Tan has denied the charges against him at his trial, which concluded last Wednesday without a ruling.

Read more at the Associated Press.