1May 1995 and1May 1997, two thallium salt poisoning incidents occurred in Tsinghua and Peking University respectively. Except for suspected man-made crimes, thallium salt is not managed according to drama drugs. Among them, Zhu Ling, a girl from Tsinghua, was permanently disabled, and the case has not been solved. In June 2007, three students of China University of Mining and Technology (Xuzhou) were poisoned by thallium.