Chen Man, 52, during his retrial at a court in Hainan province on Dec 29. Chen is hoping to prove his innocence after serving 16 years in jail for murder and arson.

He, who has spent more than 10 years studying cases of wrongful conviction, said that while physical torture, such as beating, has been brought under control, the police still use psychological coercion, such as sleep deprivation and threats, to obtain confessions.

"Judicial experts are studying ways to prevent and outlaw this type of mental torture; this is a hot, urgent issue in enforcing the rule of law," he said, adding that the legal definition of torture should be updated as soon as possible.

Yuan, the legal researcher, said the courts need to ensure that the records of interrogations provided by the police are accurate: "In some counties, the police only made a record after the suspects had confessed, or they only recorded certain parts of the confession."

Although he welcomed the moves to improve interrogation skills among officers, he warned that the police should avoid the practice prevalent in the United States, where suspects are often asked leading questions designed to prompt predetermined answers.

"Leading questions may result in false confessions that have the potential to bring about miscarriages of justice," said Yuan, who worked from 2012 to 2013 with The Innocence Project, a non-governmental organization in the United States founded to overturn miscarriages of justice and exonerate those who have been wrongfully convicted, especially via DNA evidence.

He urged similar organizations in China to make concerted joint efforts to eradicate torture and correct judicial mistakes.

Luo Yaping, a professor at the People's Public Security University of China who specializes in the study of investigative skills, said the police's ability to collect evidence at crime scenes has improved greatly, and most officers understand that the collection of legally admissible evidence is the key to reducing the number of miscarriages of justice.

"However, the lack of officers in grassroots police stations makes it hard for them to investigate cases, because the extra workload leaves little time for them to review their procedures and actions," she said.

"Investigation is the first step in dealing with a criminal case. If that first step is inadequate, the procedures that foll-ow will also be affected to a greater or lesser degree."

Contact the writer at caoyin@chinadaily.com.cn