A procurator shows visitors an electronic data identification equipment during a Beijing People's Procuratorate open day in Beijing, Dec 6, 2013. [Photo by Cao Boyuan for chinadaily.com.cn]

Zheng Hongqiang has been to many IT centers, but he never imagined visiting a digital laboratory used by Beijing's top prosecuting authority.

The 50-year-old, a fan of electronic products, was invited on Friday along with about 60 other residents to a Beijing People's Procuratorate open day, which is usually held at the beginning of December.

The lab fascinated the visitors, with such things as equipment that can retrieve deleted information from cellphones.

"I was excited to visit the authority and never thought equipment in the lab could be so advanced," Zheng said.

The lab, established in 2008, is on the fifth floor of the procuratorate building, covering about 50 square meters.

To date, more than 30 prosecutors, including 13 judicial appraisal experts and 23 assistants, have worked with digital evidence in more than 200 cases, said Zhao Xianwei, a prosecutor who is responsible for the lab.

Digital data has been the subject of legislative studies in countries, including the United States and Canada. It has been part of the revised Chinese Criminal Procedure Law since Jan 1.

Text messages and chat recordings on instant-messaging service WeChat have become important in criminal cases in recent years, especially cases involving corruption, "which is why we built up the lab to study them", Zhao said.

In one case, prosecutors obtained key information from a hospital database. A nurse, surnamed Wang, was suspected of embezzling public funds - more than 300,000 yuan ($49,260) - according to the authorities.

"If we can master more digital evidence, we'll be able to solve more cases in which it is difficult to get confessions from suspects or defendants," he said, adding that the number of cases requiring analysis of digital data has jumped 60 percent year-on-year.

The collected digital evidence is recorded on disks and then reserved in case files after being presented in courts, Zhao said.

Liu Zheng, another prosecutor at the lab, said data is copied first to ensure that original information is complete and safe.

"We can get information on cellphones, including messages and voice recordings - even what has been deleted by users," he said. "We can also trace and retrieve evidence from micro blogs, online forums, websites and e-mails."

Encrypted documents can also be opened on computers in the lab, he said.

Similar labs will be created for grassroots prosecuting bodies, including Fangshan district and No 2 Intermediate People's Procuratorate, the prosecutors added.

However, the two confirmed they still had to ask for help from social media technology associations at times.

"After all, we're not as professional as specialists in the IT industry and have much to learn, such as how to repair hard disks," Zhao said.

A woman in her 50s, surnamed Wang, said her first visit to the prosecuting authority left a good impression.

"I thought prosecutors' work was a mystery before, but now I know how they tackle a case and what the investigating procedures are," she added.

Zheng, the electronics fan, said he thought an open day should be offered more frequently.