Zhu Ling was an energetic, smart young woman before the poisoning incident. Provided to China Daily

One of the reasons that the Zhu case has attracted so much attention from the public and the media is that it is still unsolved, she added. "From a psychological point of view, the uncertainty produces greater instability than incidents that are resolved."

What's more, the incident changed Zhu's life irrevocably, ruining her promising future and causing huge damage to her health. People tend to sympathize with the weak, and Zhu's current poor health has won her a great deal of support, said Lin.

The petitioners' behavior and the reaction it provoked shows why public sentiment should never take the place of the law, said Dong Yan, an assistant professor at Renmin University of China's psychology department.

She regarded the petition as a form of "herd behavior" on the Internet: "Of the 130,000 people who signed the petition, many may have simply been following a trend. It is certain that their sensational reaction has overtaken their rationality."

Zheng Zaisuo, a senior lawyer at Zhong Yin Law Firm in Beijing, said the petition and subsequent furor illustrated that the power of social media is a double-edged sword. It drew public attention to Zhu's case, which had been overlooked for nearly two decades, but at the same time stirred up irrational emotions.

"Online bulletin board sites and weibo (social networking sites) are flooded with rumors, angry comments and curses," he said. "These angry people think they are protecting one person's rights, but they may be harming another's rights at the same time. It is the law, not people's emotions, that convicts a criminal."

"If you advocate reinvestigating a case and that unearths the culprit, you are a responsible citizen, but if you accuse Sun of murder without evidence, and call for revenge, you are just one of the mob," said Zheng.

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