A local court in Zhongshan city, South China's Guangdong province, has exempted a man who had stabbed his neighbor to death from criminal punishment after the attacker was evaluated as mentally ill.

The case is rare in China, as designating a murderer as mentally ill usually attracts great criticism from the public, who traditionally believe that a death should be paid for by a death.

The Intermediate People's Court of Zhongshan on Tuesday announced that it had ruled that Long Long (alias), a 21-year-old native from Hunan province, did not have to take criminal responsibility for stabbing his neighbor Chen Xiaobo to death, the Southern Metropolis Daily reported on Wednesday.

But the court ruled that compensation of 247,000 yuan (US$37,490) should be paid to the victim's family.

At about 9 pm on Sept 29, 2009, Chen's family were watching TV at home in Huoju district of Zhongshan, when Long knocked on their door and then had a dispute with the family because he thought Chen's two young children were making too much noise, the report said.

Long then suddenly took out a knife and stabbed Chen in the chest. Chen died later in hospital despite emergency treatment, it said.

After Long was arrested, a judicial assessment decided that when he committed the crime he was suffering from schizophrenia. Therefore prosecutors did not bring the case to court.

According to China's criminal law, mental patients can be exempt from criminal punishment if they commit a crime while they are not able to recognize or control their behavior.

However, Chen's family were unsatisfied with the result. "Long looked perfectly normal. If he had mental problems, we could not have been neighbors for two years," Li Xiumei, Chen's wife, said.

So Li appealed to the Intermediate People's Court of Zhongshan in September 2010, asking it to find Long guilty and demanding 1.36 million yuan in compensation.

During the process, Li also asked the forensic institution under the Guangzhou-based Sun Yat-Sen University to do a second assessment of Long, which found that he had limited ability to control himself and should bear partial criminal responsibility.

However, the prosecutors said the finding of the forensic institution under Sun Yat-Sen University did not have legal standing, as the institution was not authorized by the provincial judicial system.

Dealing cautiously with the case, the court then had two other judicial assessments of Long done at different forensic institutions, both of which concluded that Long should be exempted from criminal punishment.

"The assessment result affects a person's life, so we must be very careful about it. Four assessments for a single suspect is a record for us," Duan Wensheng, the judge, said.

"It's a difficult decision for us. We feel sorry for Chen's family, who may face great difficulties in the future," he said. "But we can't ignore the legal right of the suspect."

The court also ruled that Long's family should take better care of him. The Ministry of Health said in 2009 that more than 56 million patients with various mental illnesses in China had not received treatment. Only a quarter of patients with serious mental disorders are hospitalized.