A woman sentenced to life in prison for poisoning children was acquitted on Monday, renewing long-standing questions among judicial experts about the best way to ensure that legal processes are used in handling cases.

The central government determined two years ago to rectify wrongful verdicts.

Qian Renfeng was given a life sentence in 2002 by Zhaotong Intermediate People's Court in Yunnan province, after she allegedly put poison in the food of children at a kindergarten where she worked. One of the children died. At the time, Qian was 17.

The court said Qian poisoned the children because did not get along with her employer.

After serving 13 years in prison, Qian, now 30, was pronounced innocent by the Yunnan Provincial High People's Court on Monday, because evidence in the case was flawed, as was her confession.

"The evidence presented by the police was tainted, and there were some inconsistencies in the defendant's confession. Also, signatures on three statements in which she confessed to the crime were proved not to be hers," the court in Yunnan said.

Gao Wei, vice-president of the Yunnan University Law School, said that it's a must to root out improper procedures in dealing with cases, "because in this way we'll avoid wrongful judgments effectively".

It was not the first time the country's courts have overturned a judgment in the past two years.