The main suspect after police investigation is Sun Wei (孙维) (born ), who was Zhu Ling's classmate and roommate in Tsinghua University from 1992 to 1997. Tsinghua University also said Sun Wei was the only student who would have had official access to thallium compound among the students with close relationship to Zhu Ling, according to Zhu Ling's lawyer, Zhang Jie. The authorities refused to release the results of their investigation to Zhu Ling's parents after they appealed. However, Tsinghua University denied to issue Sun Wei's B.S. certificate and refused to provide her a document needed to get a passport or visa in 1997. It is believed Sun Wei has changed her name to Sun Shiyan (孙释颜).