The newly appointed attorney for poisoning victim Zhu Lingling filed an official request  Thursday to the Beijing Public Security Bureau (PSB) asking for disclosure of the documents related to the unsolved case.

Li Chunguang, executive director of Yunnan Lingyun Law Firm, who agreed to represent the victim on Tuesday, told the Global Times it was "illegal and unacceptable" for the bureau to close the case without offering Zhu's parents a formal report of the reason for the closure.

The PSB filed a document in 2007 saying that poisoning case was closed in 1998, while Zhu's family was only informed of this in 2009, Li said.

"It's ridiculous and unprofessional for the PSB to just randomly drop the case. Zhu's family and I request a continuation of the investigation," he said, adding that he is preparing for civil actions against certain entities. He declined to disclose more details.

He also asked the PSB to disclose the security classification of the information gathered during the investigation, and how long police intend to keep the information confidential. 

Then a student at Tsinghua University, Zhu was poisoned in 1994 by thallium and left permanently paralyzed. Zhu's roommate, Sun Wei, was speculated to have orchestrated the poisoning but was never convicted, allegedly due to her family's strong political connections.

Beijing police released a statement on its Sina microblog Wednesday saying that it had failed to solve the case due to a lack of evidence to convict the suspect, as the case was only reported to the police six months after Zhu was poisoned.

The People's Daily published an op-ed piece Thursday saying that timely disclosure of information is the best method to build up authorities' credibility and dispel rumors.

Despite the police acknowledgement of its failure, many Web users are still calling for the case to be reopened. 

It will be extremely difficult for police to make any  breakthroughs as nearly two decades have passed, said Han Yusheng, a criminal law professor at Renmin University of China.

"The police have to obtain evidence about the source of thallium and how Zhu was poisoned before they can convict a suspect," said Han.

"While they have advanced technologies now, they can't travel to the past to get the vital evidence that was destroyed in the past 19 years," he said.

Sun Yuan, a criminal law professor with the China Youth University for Political Sciences, said it still might be possible to uncover evidence.

"The police should restart the investigation… the difficulties of gaining evidence shouldn't be the sole reason not to reopen the case," he noted.