Ai suffered headaches and claimed he had difficulty concentrating on his work since returning from Chengdu in August 2009, where he was beaten by the police for trying to testify for Tan Zuoren, a fellow investigator of the shoddy construction and student casualties in the earthquake. On 14 September 2009, Ai was diagnosed to be suffering internal bleeding in a hospital in Munich, Germany, and the doctor arranged for emergency brain surgery. The cerebral hemorrhage is believed to be linked to the police attack.