BEIJING -- The policeman yanked the black hood over Ai Weiwei's head. It was suffocating. Written in white across the outside was a cryptic phrase: "Suspect 1.7."

At the rear of a white van, one policeman sat on each side of Mr. Ai, China's most famous artist and provocateur. They clutched his arms. Four more men sat in the front rows.

"Until that moment I still had spirit, because it didn't look real," Mr. Ai said. "It was more like a performance. Why was it so dramatic?"

On the morning of April 3, 2011, the policemen drove Mr. Ai, one of the most outspoken critics of the Communist Party, to a rural detention center from Beijing Capital International Airport, where Mr. Ai had planned to fly to Hong Kong and Taiwan on business. So began one of the most closely watched human rights dramas in China of the past year.