A medical student at Shanghai Fudan University was poisoned on April 1 and has been in critical condition since.

Police say one of his roommates is their top suspect and is questioning him.

The student appeared unwell on April 1. His condition worsened after being transferred to the university hospital, showing symptoms of liver failure, said the university in a statement on Monday, without giving his name.

The cause of his sickness hasn't been determined, said the statement. He is currently receiving medical treatment at Zhongshan hospital in Shanghai.

Police found toxic compounds in residual water from the water fountain in his dorm on April 11, and questioned his roommate the next day.

The case is still being investigated.