No remorse: The 'potential psychopath' behind the South Yorkshire attacks

The attacks that shocked Britain: Full coverage

Child protection expert Dr Eileen Vizard told the judge the boy, who carried out the attack when he was just 10, was a "very high risk" to the community.

Dr Vizard, a consultant child and adolescent psychiatrist, said the boy had shown no remorse and hardly any empathy with his victims during her assessments of him.

She told the judge sentencing two brothers accused of a serious attack on two other boys how she had spent some time with the younger of the two brothers.

She said she had produced three reports on the boy, who is now 11.

Giving evidence in the middle of the prosecution opening, Dr Vizard told the court: "I have assessed (the boy's) risk to the community as being very high."

She went on: "Firstly, a risk of serious violence. Secondly, a potential risk of sexual assault. And, linked with that, a risk of sadistic behaviour."

Dr Vizard said what she had studied about the youngster led her to the conclusion he was a "risk to a range of people in the community from quite young children through to older people and, furthermore, males and females."

The expert said she took into account the boy's history of "extremely worrying" behaviour, saying he had been "roaming the community and targeting the community, including a young child - a foster child, a very, very young child, two or three years old - right through to children the same age, right through to older children, adult women and, as I said, both genders".

Dr Vizard said the boy was in danger of developing Anti Social Personality Disorder when he became older. She said he was too young to be diagnosed with this at the moment.

She went on: "He's a young person who had started anti-social behaviour long before he was aged 10, according to all the records."

The doctor said she noted a series of worrying aspects to his attitude in her contacts with him which were indicative of psychopathy - psychopathic behaviour.

She said he demonstrated "callous, unemotional traits" and "showed very little, hardly any empathy for his victims".

She went on: "He certainly showed no remorse and didn't have much insight into why he behaved in this way."

Dr Vizard said his record of anti-social behaviour "shows him to be at risk, without appropriate help, of being one of the minority of seriously disturbed, psychopathic offenders".

The doctor detailed his "unusual behaviour" when she met him with a colleague, saying he developed a threatening attitude which was "intimidating" despite his age.

She said he "prowled" around the room they were in.

Dr Vizard said: "He will go on inflicting harm unless someone stops him."