How did Sister Zhu Ling, one of the top ten unsolved cases in Tianya, die?

Thallium poisoning. It is said that a suspect in a dormitory poisoned the water dispenser and went to Peking University Hospital for treatment. It was never discovered. Thallium poisoning was discovered later, and it took too long to treat it with corresponding methods. Last year, the suspect immigrated to the United States and was jointly signed by Americans on the White House website, prohibiting his entry.