Conversation so far:
what is release referring to with Ai Weiwei?
On 22 June 2011, the Chinese authorities released Ai Weiwei from jail after almost three months' detention on charges of tax evasion.
what evidence did the Chinese authorities have on Ai Weiwei in regards to tax evasion charges?
Professor Wang Yujin of China University of Political Science and Law stated that the release of Ai Weiwei on bail shows that the Chinese government could not find any evidence.
how was Ai Weiwei treated in prison?
On 24 June 2011, Ai Weiwei told a Radio Free Asia reporter that his detention by the Chinese regime was hellish, and is forbidden to say too much to reporters.
what did they do to Ai Weiwei in prison?
After Ai Weiwei's release, his sister gave some details about his detention condition to the press, explaining that he was subjected to a kind of psychological torture.
was Ai Weiwei subjected to any other mistreatment?
Chinese authorities again investigated Ai Weiwei and his associates under the charge of spreading pornography. Ai's wife, Lu Qing was questioned by police, and released. The exact charges remain unclear.
What was Ai Weiwei charged with when Chinese authorities against investigated Ai Weiwei and his associates under the charge of spreading pornography with Ai's wife, Lu Qing, being questioned and relead, and the exact charges remaining unclear?
Chinese authorities again investigated Ai Weiwei and his associates under the charge of spreading pornography. Ai's wife, Lu Qing was questioned by police, and released. The exact charges remain unclear.
what did the public think of Ai Weiwei's imprisonment under the charge of spreading pornography?

Question: did they have evidence against him?
Self-contained rewrite: did the Chinese authorities have evidence against Ai Weiwei for charges of spreading pornography?