The 30-Year Unsolved Case:The Tsinghua Poisoning Incident of Zhu Ling

Zhu Ling, a native of Beijing, enrolled at Tsinghua University in 1992. In 1994 and 1995, she was deliberately poisoned twice with thallium, a lethal chemical, resulting in symptoms such as paralysis, neurological damage, and lifelong disability.

On May 1, 2024, the WeChat public account “朱令我们在一起” (Zhuling, We Stand Together) reported new developments in the “Tsinghua Thallium Poisoning Case.” Recently, the Supreme People’s Procuratorate accepted the “Investigation Supervision Application” submitted by Zhu Ling’s parents.

According to the report, Zhu Ling’s mother received an SMS notification from the Supreme People’s Procuratorate: “Zhu Mingxin: Hello! We have received your letter. According to relevant laws and regulations, our institute has forwarded your letter to the Beijing Procuratorate for review and handling.” Subsequently, Zhu’s mother received another notification from the Beijing Procuratorate: “Zhu Mingxin, hello! Our institute has received the petition materials assigned by the Supreme People’s Procuratorate and has forwarded them to the relevant department for handling. Contact number: 0105876XXXX. You can check it through the online procuratorial service center after one day.”

In April 2024, Zhu Ling’s father, Wu Chengzhi, confirmed to Southern Metropolis Daily that he had submitted the “Investigation Supervision Application” to the Supreme People’s Procuratorate via mail on April 15, requesting a reopening of the investigation into Zhu Ling’s poisoning case.

Zhu Ling passed away in Beijing on December 22, 2023. On December 23, Professor Yan Feng of the Chinese Department at Fudan University in Shanghai expressed on Weibo: “Zhu Ling is gone. Thinking of her thirty years of unjust suffering, unspeakable pain, and untraceable justice, my heart is filled with sadness and indignation. Some of her Tsinghua classmates have been trying their best to take care of her and her parents. There is hatred in this world, but there is also love. May the deceased rest in peace, and may the living be safe.”

Thallium poisoning is a common type of murder case. In the past few decades in China, the Zhu Ling case undoubtedly had the greatest impact, without comparison. So why has this highly publicized murder case not been resolved to this day? What secrets lie behind it?

In October 1994, Zhu Ling, a student majoring in physics, chemistry, and instrumental analysis at Tsinghua University, began experiencing strange symptoms such as pain, dizziness, hair loss, and vision deterioration. She sought medical treatment multiple times at Beijing Union Medical College Hospital, China’s top hospital, but to no avail. Over several months, her condition remained undiagnosed. After a slight improvement in January 1995, Zhu Ling was discharged but relapsed with more severe symptoms a month later, requiring hospitalization again. By March of that year, her condition had become critical, and Union Hospital was unable to offer an effective treatment plan, leading to Zhu Ling falling into a coma for six months.

Despite doctors suggesting thallium poisoning, similar to cyanide but caused by a rare metal, Union Hospital claimed it lacked the facilities to test for thallium poisoning.

On April 28, 1995, after Zhu Ling was diagnosed with thallium poisoning, her parents immediately filed a case with Tsinghua University, suggesting foul play. However, Tsinghua University officials delayed reporting to the Beijing Public Security Bureau for seven days, finally filing a report on May 5. Strange events followed as Zhu Ling’s dormitory was later involved in a theft case, with many of her personal items, including items that could have been evidence of poisoning, mysteriously disappearing.

To be frank, as a former detective, I believe cases of poisoning like this one are not difficult to solve for two reasons. First, the source of thallium can be traced. Ordinary people simply do not come into contact with it, so the group of people who can access thallium is extremely small and well-defined. Second, Zhu Ling had a simple social circle—just classmates and family. Whoever used poisoning, an inconspicuous method, to harm her must have been someone she knew well, familiar with the properties of thallium. When these two small circles overlap, the suspect can be identified almost conclusively.

At the time, there were only about twenty institutions in all of China researching thallium, with only Tsinghua University’s Chemistry Department having a laboratory that handled thallium compounds. Among Zhu Ling’s friends and family, only her dormitory roommate, Sun Wei, had the possibility of exposure to thallium, as the lab at the time contained a thallium compound. Zhu Ling, originally named Zhu Lingling, hailed from an intellectual family—her father was a senior engineer at the China Earthquake Administration. Zhu Ling once had a sister who was a Peking University student but tragically died in a spring outing accident in 1989, leaving her as the sole child in the family. Zhu Ling received an excellent education from a young age and lived up to expectations by gaining admission to Tsinghua University. A multitalented individual, even among the academic elite of Tsinghua, she stood out. She played the piano, guqin, and guzheng, joining Tsinghua University’s folk music band during her university years and becoming a key player. In 1994, she received the second prize in the National College Art Performance Solo Group. In addition, her physical health was superb—she was also a Beijing swimming athlete. Before the poisoning case, she was an outstanding figure who was envied by everyone.

In such an environment in China, a talented person is also envied while being admired, and this is highly probable.

On March 25, 2002, another one of Zhu Ling’s classmates, Bei Zhicheng, used his real name to post an article entitled “Some Situations in the Zhu Ling Case” on the New Silk Language Network. It exposed how Sun Wei, Zhu Ling’s roommate, and Sun Wei had previously squabbled over the opportunity to play the guzheng in the university’s folk music group. At the time, Sun Wei lived with three other people in the same dormitory as Zhu Ling: one was a Mongolian girl from Xinjiang, Jin Ya, the second was a girl from Baoji, Shaanxi, Wang Qi, and the third was Sun Wei, also from Beijing. They all majored in physics, chemistry, and instrument analysis and were classmates. Even though they were classmates, everyone had their own research topics, and different topics were dealt with in various chemical labs. Because Sun Wei had her own research topic, she was the only student capable of handling thallium salts in the had study been are had.As I mentioned earlier, Zhu Ling was poisoned twice. The first time, her symptoms were relatively mild, and she was discharged after a month. The second time, due to inexplicable misdiagnosis at Peking Union Medical College Hospital, she suffered severe disability, becoming vegetative. The two poisonings were a month apart. To carry out this poisoning without detection, there were two conditions:

First, familiarity with Zhu Ling’s lifestyle, knowing what she liked to eat and drink. Second, the ability to access Zhu Ling in her daily life and successfully poison items she regularly used. So, how did the Beijing police handle this seemingly straightforward case?

The case was filed by the Beijing Public Security Bureau in May 1995, but no effective investigation measures were taken afterward. There was no effort to search for Zhu Ling’s mysteriously missing personal items, no forensic examination of places like her dormitory or laboratories, and not even questioning of suspects. It wasn’t until seven months after the incident, at the end of 1995, under constant pressure from Zhu Ling’s parents, that the Beijing police finally responded, claiming they had suspects. However, by February 1996, they informed Zhu Ling’s parents that the case was difficult to solve and still under investigation.

It wasn’t until two years after filing, on April 2, 1997, with continued complaints from Zhu Ling’s parents, that the Beijing Municipal Public Security Bureau first questioned the prime suspect, Sun Wei. Astonishingly, they released her home just eight hours later. This was the first and only interrogation conducted by the Beijing police on Sun Wei, the primary suspect in such a serious poisoning and murder case, two years after initiating the investigation. What kind of operation was this?

Sixteen years later, in May 2013, under public scrutiny, the Beijing Municipal Public Security Bureau finally responded to investigation inquiries on their official microblog “Ping An Beijing.” They claimed to have conducted interviews with over 130 relevant individuals and inspected over 100 units in Beijing using thallium salts. However, they remained silent on the most crucial findings of the investigation. The reality was that on August 25, 1998, the Beijing police met with Zhu Ling’s parents, notifying them that due to insufficient evidence, the case was closed without resolution. They did not inform Zhu Ling’s parents that the case had been closed, nor did they disclose this information publicly. Zhu Ling’s parents remained unaware until April 20, 2013, when a Beijing newspaper, “The Beijing News,” revealed that the police had long since closed the case.

As early as May 2008, Zhu Ling’s family, suspicious of the Beijing police, requested disclosure of the investigation process and results. However, the Beijing police issued a government notification stating that they could not disclose the information due to legal regulations. Despite a municipal government review in March 2009 mandating the police to disclose information, the Beijing Public Security Bureau ignored the directive. Responsible for the case was the 14th Division of the Beijing Municipal Public Security Bureau, specifically the Cultural Protection Division, specializing in university cases. The officer in charge was Li Shusen, who, in a 2006 interview with “Southern People Weekly,” implied:

“From Li Shusen’s words, what can we infer? There are hidden difficulties. How could such a simple poisoning case be hastily closed by the Beijing police? What mysteries lie behind this?”

Intelligent people might suspect that Sun Wei, the prime suspect, is not an ordinary person. Indeed, her family background is notable. Sun Wei’s grandfather, Sun Yueqi, was a prominent figure during the Republic of China era, a veteran of the Kuomintang, highly esteemed by Chiang Kai-shek, and served as Minister of Economy and Chairman of the Resources Commission. In 1949, he led his followers and surrendered to the Communist Party of China, becoming a respected figure within the new regime. Sun Wei’s uncle, Sun Fuling, served as Deputy Mayor of Beijing from 1983 to 1993 and as Vice Chairman of the National Committee of the Chinese People’s Political Consultative Conference from 1993 to 2003, a high-ranking official.

Sun Wei’s father, Sun Dawu, also served in the Central Committee of the Revolutionary Committee of the Chinese Kuomintang and was the legal representative of Beijing Taiyang Electronics Technology Co., Ltd. Despite not being part of a “red” family, the Sun family’s historical connections, especially their relationship with Jiang Zemin, facilitated their high status. During the poisoning incident, which occurred during Jiang Zemin’s presidency, Sun Wei’s close ties to Jiang Zemin suggest that she had connections at the highest levels.

There were online rumors that before Sun Wei’s grandfather passed away, Jiang Zemin visited him and requested not to harm his granddaughter. This case cannot be considered unsolved because of its limited suspect scope; hence, it is not difficult to investigate and collect evidence. The normal and absurd treatment of Peking Union Hospital is evident. For example, suspected Zhu Ling family test results refused to perform tests for thallium poisoning, refused to receive advice and recommendations from medical peers at home and abroad, and even refused to use the internationally recognized specific treatment, Prussian blue, and insisted on using their detoxification scheme. It is not entirely like a top Chinese medical institution should have. Secondly, the Beijing police showed no real commitment throughout the investigation, often handling the case with a dismissive attitude, minimizing its importance. As direct evidence, some items from Zhu Ling’s dormitory remained at the school after her disappearance. The public security department sealed these items as early as 1995, storing them in the chemistry department’s office and providing Zhu’s family with an inventory. Strangely, these crucial pieces of evidence requiring later analysis were never tested by the Beijing police, nor were they preserved as evidence. This neglectful handling led to a second theft of Zhu Ling’s belongings from the school three years after the initial incident, in 1998. The chemistry department of Tsinghua explained that Zhu Ling’s final personal items, including her used camera, honey, and coffee, were all lost thereafter, leaving no personal belongings of Zhu Ling as evidence.

Thirdly, there is Sun Wei’s response after the incident. On December 30, 2005, a user on Tianya Community with the ID “Sun Wei’s Statement” published an article, later confirmed by Sun Wei’s father as being from Sun Wei herself. Her article, titled “Sun Wei’s Statement Refuting Rumors Arising from Zhu Ling Thallium Poisoning Case,” was essentially a self-defense, claiming she was not the only student at the school who had access to thallium salts and portraying herself as a victim. The next day, Zhu Ling’s classmate, Bei Zhicheng, also posted an article on Tianya Community titled “Statement Regarding Zhu Ling Incident,” refuting Sun Wei’s claims and revealing further details. He stated:

“After this matter escalated on Tianya Forum, Zhu Ling’s parents once requested a face-to-face communication with Sun Wei, but Sun Wei refused.”

On March 1, 2006, Sun Wei, accompanied by her husband and brother, visited the Phoenix Club in Beijing to meet with Chen Luyu, the host of Phoenix TV, for an interview. However, the interview ended acrimoniously and was never aired.

Cao Zhixiong, the executive producer of “A Date with Luyu,” later confirmed that Sun’s family and Phoenix TV had signed a confidentiality agreement, prohibiting Phoenix TV from disclosing the content discussed. What exactly could not be disclosed?

After graduating from Tsinghua University, Sun Wei went on to work at Nokia. In early 2006, Sun Wei changed her name to Sun Shiyan and altered her birthday from August 10 to October 12, using photos from her high school days for a new ID card. Later, she remarried and moved to the United States.

On April 18, 2013, from the United States, Sun Wei, using the username “Sun Wei’s Statement,” posted another article on Tianya Community titled “After So Many Years, Like Many Others, Waiting for the Day When the Truth Comes to Light.” In the article, she said, “Drunk and lying high, singing alone. Why bother to laugh or scold.” Her attitude angered netizens.

Some American netizens launched a petition on the White House website, requesting the U.S. government to investigate and deport Sun Wei. Within just three days of its release, this petition garnered over a hundred thousand signatures of support. Although their wish was not granted, it sparked another media storm, forcing Sun Wei to leave the United States and subsequently relocate to Australia.

I do not know Sun Wei’s intentions in posting this article, nor do I know if she truly expects the truth to come out. Because if she really did, she should have visited Zhu Ling when she was ill, after all, they were classmates who shared the same dormitory. During her many years in China, she had ample time and opportunities to explain things to Zhu Ling’s parents, but she did nothing except hide on the edge of the Internet, constantly trying to whitewash herself.

The law and power may forgive a criminal, but conscience does not. I believe that wherever the true culprit may hide, whether in the United States or Australia, Sun Wei will carry the label of a suspect for the rest of her life. This label, even after her death, will never disappear.