But in one encouraging sign for Zhu Ling’s supporters, the topic has been unblocked on Sina Weibo, China’s most popular microblog service, suggesting that high-level officials have decided that suppressing the controversy is counterproductive.

Still, the case has become something of a public relations challenge for China’s new leadership. In the five months since he was appointed Communist Party secretary, Xi Jinping has been trying to address rampant public cynicism by attacking official corruption and the abuse of power, although most of those efforts have so far been widely viewed as superficial.

In one especially ham-handed attempt to grapple with the controversy, Global Times, a bilingual tabloid published by the party-owned People’s Daily, said in an editorial that public indignation over the Zhu Ling case was largely the result of poor communication by the authorities. But the editorial acknowledged that the truly powerful can influence the criminal justice system by insisting that Ms. Sun’s family “was not distinguished enough” to have such sway.

The accused has remained out of public view these past two decades, although after her name began to spread across the ether in 2005, she posted a brief online defense, saying she was innocent and in fact also a victim because of the unfounded accusations against her. “On the Internet, even though everyone is just a virtual ID, one should still be rational, objective and responsible for their own words and actions,” she wrote.

The case has provided a fascinating showcase for the power of the Internet. It was in early 1995, after Ms. Zhu’s illness stumped doctors at one of Beijing’s premier hospitals, that a desperate high school classmate posted a cry for help on one of the few wired computer terminals then available in China. Amid the hundreds of replies from Western medical experts, most correctly identified the syndrome as thallium poisoning and suggested the antidote — a commercial dye known as Prussian blue.

The information saved Ms. Zhu’s life, but she remains severely disabled, her aging parents forced to tend to her round the clock. Ms. Zhu’s 72-year-old mother, Zhu Mingxin, has said she is not willing to give up, despite the authorities’ refusal to reopen the investigation. “In the prime of her youth she nearly lost her life, and she’s been miserable ever since,” she told China National Radio earlier this week. “I hate the perpetrator.”

In recent years, the family has been receiving help from an American-based nonprofit group that has been raising money and reminding people that the crime remains unsolved.