A judge is calling for a public debate on the need for special courts to hear cases involving mentally ill children. The proposal was made yesterday at the trial of a boy with severe psychiatric problems, who admitted killing his six-month-old brother by repeatedly stabbing him and cutting off his hand.

A judge is calling for a public debate on the need for special courts to hear cases involving mentally ill children. The proposal was made yesterday at the trial of a boy with severe psychiatric problems, who admitted killing his six-month-old brother by repeatedly stabbing him and cutting off his hand.

The 12-year-old, who suffers from Asperger's syndrome, a type of autism rarely associated with acts of violence, cannot be named for legal reasons. Bristol Crown Court was told that he had walked into a police station in January last year and confessed to stabbing his brother.

The police immediately went to his home, to find his mother unaware of what had happened. Upstairs, the baby was discovered in his cot with 17 stab wounds and his left hand severed.

Roderick Denyer QC, for the prosecution, said the boy had admitted getting a kitchen knife after his brother began crying as he tried to feed him. "When I got the knife I was thinking to hurt [the baby]," the boy said. "I was in the room for a couple of minutes. I was aiming to hurt him. I don't know why."

During yesterday's hearing, court formalities were dropped, with judge and lawyers abandoning their wigs and gowns.

Mr Denyer told the court the Crown Prosecution Service accepted the plea of manslaughter by reason of diminished responsibility. Helena Kennedy QC, for the defence, called for the case to be adjourned for further psychiatric reports. It was important, she said, for the court to understand why the killing had taken place.

The judge, Mr Justice Toulson, said the case raised questions about the current legal system's ability to try children, and in particular those with a mental illness, in serious cases. "It does seem to me there is a need for very real public debate in cases of... grave wrongdoing, whether they wouldn't be better dealt with in specialist courts," he said.