BEIJING — She was a promising student at Beijing’s prestigious Tsinghua University, a talented musician who loved to swim and dreamed of studying German and computer science.

But in her sophomore year, Zhu Ling began suffering acute stomach pain and hair loss, eventually becoming severely disabled. Lab tests showed she had been poisoned with thallium, a toxic metal used in rat poison, but police made no arrests and quietly closed the investigation.

Today, 19 years after Zhu first fell ill, she remains paralyzed, nearly blind and has the mental capacity of a child. And her case is suddenly generating a firestorm on the Internet in China and elsewhere, highlighting the Chinese public’s anger over perceived injustices, the powerful force of social media and the deep pain of a family that for two decades has sought answers from secretive authorities.

Lack of transparency and police disregard of people’s rights often trigger protests in China, online and in the streets.

Last Wednesday, police swarmed a clothing market area in the southern section of Beijing to shut down a demonstration, possibly the largest in the capital since 1989, involving hundreds of people after the death of a migrant worker that police ruled a suicide. Authorities quickly quelled the unrest by making concessions to the family of the dead 22-year-old woman.

The sad story of Zhu Ling has been publicized before, but a surge of online sympathy arose after the news last month of the poisoning death of a Shanghai university student.

In recent days, China’s Twitter-like service, Sina Weibo, and other microblogs have been flooded with posts demanding that the case be reopened. Many allege that Zhu’s roommate, now believed to be living in the United States, was behind her poisoning but that police dropped the matter because the roommate’s family was politically connected.

The activism has gone abroad as well, with more than 130,000 people signing a petition on the White House website urging the U.S. to investigate and deport the suspect.

Chinese government censors, always mindful of anything that could trigger social unrest, deleted references to Zhu Ling on Weibo for a time, but the ban was lifted last Monday as authorities apparently deemed the cyberspace protest manageable.

Then, on Wednesday, Beijing police issued the government’s first public statement on Zhu, denying there was any outside interference and expressing regret that the crime was unsolvable because of a lack of direct evidence.

Zhu’s family lawyer, Li Chunguang, said in an interview Thursday that the statement merely raised more questions. He said police told the family in 2007 that authorities received the case two months after Zhu was hospitalized, but the statement said it wasn’t until nearly six months later. If not direct evidence, what indirect findings did police have from the more than 130 people they said crime experts had interviewed?

“The first priority is, if you can, find the (suspect), but if that couldn’t be done, at least you can show us the detailed investigation procedure,” Li said, noting that it wasn’t until 2007 that Zhu’s family learned that police had closed their investigation in August 1998. Li said he was prepared to bring legal action against the government, however fruitless that might be. “We want to know the truth,” he said.

Zhu’s case was mysterious from the start. When she was hospitalized in late 1994, doctors couldn’t figure out what was wrong.

It wasn’t until early the next year that Zhu’s friends, tapping what was then China’s very limited Internet connectivity, sent online requests for help to the medical world outside, according to accounts from Zhu’s classmates. Many doctors replied that the likely cause was thallium poisoning, but by then Zhu’s condition had deteriorated sharply.

Beijing’s public security bureau statement said that the diagnosis was made April 28, 1995, and that Tsinghua University reported it to police on May 5, after which a team of experts was immediately assigned.

In China’s blogosphere, many point the finger at Zhu’s former roommate, Sun Wei, identified as Jasmine Sun in the White House petition. (The White House declined to comment on the petition except to say that it reviews all petitions that receive enough signatures; the threshold is 100,000.)

Sun was questioned by police, but they took no further action, according to the state-run China Daily.

But the ire directed at Sun could also stem from the fact that she is the granddaughter of a powerful industrial leader, the late Sun Yueqi. Children of the elite are widely perceived as enjoying special privileges.

The Los Angeles Times was unable to reach Sun’s family, including her father in Beijing, for comment.

The sympathy for Zhu is rooted in anger over injustice, said Zhao Jing, a closely followed blogger in Beijing who uses the pen name Michael Anti. In particular, he added, “it’s an echo from that kind of rage against the guan er dai,” a mocking reference to the “second generation” of officials, those who are descendants of powerful cadres in China.

Li, the family attorney, said Thursday that “police have a responsibility to give an answer on Sun Wei, whether she was a real suspect. I think it’s also for Sun Wei’s sake.”

The lawyer, who said he started to represent the Zhu family last Tuesday, knows it will be difficult to make the investigation results public. But in recent years, he said, the Chinese legal system has been paying more attention to the rights of victims, in no small part because of activism on the Internet.

“The family has been helpless for so many years, before the recent attention on Weibo,” said Li, who is from the southern city of Kunming. “And it all started with that (poison) murder case at Fudan University” in Shanghai. In that case, police quickly arrested the victim’s roommate.

Though China’s online vigilantism makes some people nervous, Zhan Jiang, a communications professor at Beijing Foreign Studies University, sees the attention on Zhu generated by social media as a healthy sign, even though such cases carry risks for the central government.

“If you continue to repress this, it won’t stop it,” he said of the short-lived blocking of discussion on Zhu. “This case will give an opportunity and be helpful for the rule of law to go one step forward.”

For Zhu’s parents, who are now in their 70s and spend their days and nights taking care of their daughter, there is little solace in all the Internet attention.

“She has always brought me happiness since she was little,” Zhu’s mother, Zhu Mingxin, said in an interview last week with China National Radio. “If everything went as we had planned for her, I’m sure she would be doing a great and I would be really happy for her. But now, all is lost.”