The prisoner with no name is up by seven every day with the 18 other inmates of his unit. His room has a bed, and a desk, and a toilet. He eats breakfast and gets ready to go to school, where for five hours he has a teacher to himself. Then there is gym, often basketball, and dinner, followed by parental visits.

Probation officer Terrence Starr, who oversees the Contra Costa Juvenile Hall, had to lay on special equipment for his newest ward: Lego and a teddy bear. "In many ways he's absolutely another six-year- old," Mr Starr said. "Our job is to try and give him whatever chance he's got coming, and try and protect the rest of us at the same time."

The charges facing this boy, whose feet dangled from his courtroom chair, are that he did, with malice aforethought, attempt the unlawful killing of a one-month-old baby boy, in the commission of the burglary of a bright blue Big Wheel tricycle. Asked by a juvenile court judge if he understood the charges, he answered: "Yeah".

Download the new Independent Premium app Sharing the full story, not just the headlines

He is believed to be the youngest ever accused of attempted murder in the United States. The boy nearest his age at the detention centre is 13. His defence attorney Leslie Bialik says of him that he "seems like a little kid, a little munchkin". Child psychologists say it is absurd to charge one so young with a serious crime. And even the family of his alleged victim say they want to see him in care, not in juvenile detention.

But prosecutor Harold Jewett, who brought the case, has a no-nonsense reputation in Richmond, California, a small town 20 minutes drive north of San Francisco. It is in no one's interest, he told a court, to "put this minor in a faculty where he has any freedom of movement at all".

"We have evidence," he repeats for the umpteenth time, talking like a London policeman, "that the six-year-old boy entered this home intent on stealing a tricycle, and beat a four-week-old baby with his feet, and fists, and a stick, and left with the tricycle.

"If I filed the case I do think that I can prove it," he says. "In this case the primary concern was whether or not a six-year-old knew the difference between right and wrong. I believe he did know the beating of a four-week old boy was wrong. It was patently obvious he knew what was right and wrong."

In the last 20 years the United States has moved down the age scale in defining criminal responsibility. There has been a surge in committing teenage minors for trial as adults in adult courts; the Supreme Court has upheld the death penalty for crimes committed at 16. Younger teenagers are blamed for a growing proportion of violent street crimes.

But even under English common law, on which the US legal system was based, the line for criminal culpability is usually drawn at seven, and there is a presumption against it until a child reaches 14, and in Britain, in practice, the lower limit for culpability is 10, with a presumption against it until 14. "At what point are we willing to acknowledge that children don't have the capacity to make good judgements?" asks Jeffrey Butts of the National Centre for Juvenile Justice, a private research group. "At what point are we going to stop this rush to take away the status of childhood for children?"

The accused would-be killer and his alleged victim, Ignacio Bermudez, lived within a few blocks of each other in the "Iron Triangle" in Richmond, described as a mixed race, blue collar neighbourhood, framed by the railway lines that give it its name.

Daily coronavirus briefing No hype, just the advice and analysis you need Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive morning headlines Monday - Friday plus breaking news alerts by email Update newsletter preferences

On 22 April, it is claimed, the boy entered an unlocked house belonging to a Mexican immigrant family, in the company of two friends, eight-year- old twin brothers. The baby was sleeping, and the baby-sitter, his 21- year-old stepsister, was in another room. In an attack apparently led by the six-year-old and which lasted only a couple of minutes, the infant was toppled from its crib, pummelled, kicked, and beaten with a stick.

One of the brothers claimed he acted as a look-out; it was the other, apparently, who laid the silent and bloodied baby on another bed. Then all three fled with the tricycle. Their handiwork was discovered minutes later by the baby-sitter, who says she heard nothing. The baby's skull was cracked in two places, and it was two weeks before it was removed from the critical list at a local children's hospital. Doctors say the child is likely to have suffered permanent brain damage, though they are uncertain how serious.

Amid tearful confessions from the other two boys the six-year-old, a police spokesman said, cried less than the others and lied about what happened. His companions have been charged only with burglary and released.

It is "malice aforethought" that apparently distinguishes the six-year- old, at least in the prosecutor's eyes. Two days before the attack he had brazenly walked into the house armed with a stick; the child's father, also Ignacio, had ordered him out. He "expressed the belief that the family there had been harassing him, looked at him the wrong way, and he had to kill the baby," Mr Jewett told a detention hearing. "This young man is very angry... he should not be released, period."

He allegedly threatened a female witness, telling her he would harm her if she went to the police. If convicted, he could spend up to 11 years in juvenile detention. Six is young, Jewett concedes, but the gravity of the case demands prosecution. "We did not just have the right but a responsibility, to interject ourselves as a society. This is more than a family thing," he says.

The San Francisco area, however, is going through the same debate seen in Britain over the James Bulger murder as is Chicago, where in 1994 two 10 and 11-year-old Chicago boys threw a five-year-old out of a 14th floor window. Is the accused suffering a touch of evil, is he a little monster in the making, or simply another child who needs help? Why was he roving the streets at six in the evening? Where, one psychoanalyst asks, was the empathy for a helpless little human?

Teachers say that in school he was disruptive, a class clown, and required special help, but was "never evil". Some children in the area told reporters he was cruel to animals; others that he was a bully. The novelty of life inside is wearing off for the boy, Mr Starr says, and he would like to be home. "He will adjust to it, he's a tough little kid. He's not sophisticated, he's streetwise, he's a feisty little rascal. He's not afraid of anything."

He loves basketball. In a recent game he stood on the side line with a youth counsellor who acts as referee, and made all the game calls. "Hey, that was a foul, and you didn't call it," he said. He's neither shy nor reticent, though he's well aware of being right at the centre of attention.

The probation officer Mr Starr, as he discusses the case, finds himself suddenly remembering a schoolyard thug named Jaspar. "He was the meanest kid in my life, and he was mean to everybody in the world. Boy, he used to scare the hell out of me. He was about two years older than I was, and he was real hard on the critters around there. There were people saying even then that was a crazy sign."

Later in life Mr Starr encountered - on a professional basis - a seven- year-old arsonist in San Diego, California. "Every time he would get mad with her mother he would set her clothes on fire." It made the boy "real popular" with the tenants of their building, he said. But now he is dealing with one of the youngest children he has seen in the system.

The baby's father, Mr Bermudez, in an extraordinary show of forgiveness, has said repeatedly he wishes no harm to come to the boy. "I don't want to see anything happen to that child because he also has a mother and she would suffer very deeply, just as we are suffering," he said.

In a public meeting organised by local police in response to rumours of black-Hispanic tension over the beating, the boy's mother, Lisa Toliver, who is black, hugged members of the Bermudez family. "I don't think he did it," said Ms Toliver, 27. "If he did it, he didn't know it was a baby."

The town is going through the motions of shock. The local Chamber of Commerce has opened a fund for donations for all the children. But the truth, said the head of the local elementary school, was that his pupils - who included all three boys - were not unduly traumatised by the incident. "They've gone through so much," said Marco Gonzalez. "They are victims of poverty, some are victims of crime, some are victims of bad luck."

Twenty-five years ago, it has emerged, two San Francisco brothers aged seven and 10 confessed to a far more horrific crime - the crucifixion murder of a small child. But they were never charged with a crime, instead placed in intense therapy, and a judge slammed a comprehensive gagging order on the case.

The identity of Toliver's son is well known to the media and his neighbours. But the two boys in the earlier case have never to this day been identified, not even to the family of the victim, 20-month-old Noah Alba. People still nursing the wounds from that case say they are furious with charges against the six-year-old. "This little guy didn't know what he was doing," said a close relative of Noah. "Can you imagine when he's older? Do you think he would deserve to have this brought up again?"

Police searches of his past have produced no record of abuse, but a family history of explosive violence. In 1992, his 21-year-old father was murdered in North Richmond, shot five times in the head as he reached for his own weapon. His mother's brother, aged 17, was held in the same Contra Costa Juvenile Hall where he now lives on murder charges, accused of calling a taxi then riding off and shooting the driver. He was acquitted.

His grandmother, who looked after him while his mother worked at a day care centre, has been convicted of dealing drugs. His mother has brief tangles with the law - among them sheltering her brother - but has generally managed to stay clean. The boy's actions - feuding with people who looked at him the wrong way, threatening witnesses - seem a childish mirror of many a gang killing.

According to Dr Herb Schreier, who heads the child psychiatry clinic at the nearby Oakland Children's Hospital, where the baby victim was recently removed from a ventilator, and where the boy may go for assessment, there is such a thing as a "little psychopath", or children who are prone to becoming psychopathic. Those exposed to abuse or even to the experience of violence are particularly at risk.

But what to do with a little psychopath once you've found one remains the problem. Many studies, Dr Schreier says, show that children who are jailed commit more crimes later in life than those who are released to their families, even abusive families. He, for one, is adamant: "Anybody who has any notion that sending somebody to jail is good for them is off the wall."