He was widely considered a nice boy, a regular 17-year-old studying in a high school in the historic town of Osafunecho, western Japan. Even after June 21st, when he took a baseball bat, beat four of his schoolmates, then went home and smashed his mother on the forehead before killing her with a blow to the back of the head, many who knew him still thought of him as a fundamentally decent fellow. When he was captured two weeks later in northern Japan after a dramatic 700-mile escape by bicycle, 40 local households signed a petition asking that he be treated leniently.

He later told police he got on well with his mother, but left her dying in a pool of blood because she would be disappointed in him if she learned of the earlier attack on his fellow students.

The murder should have shocked the nation, and it did, but only a little. A recent series of horrific crimes by teenagers is changing the way Japan views its youth. For decades, Japan complacently assumed it was immune from the youth violence of the United States, the country to which it obsessively compares itself.

In broad terms, that self-image is still accurate. Though serious youth crime has hit a 10-year high and arrests for murder and attempted murder by under-20s are up by one-third in the first half of this year, Japan is still very much free of violent crime. The nation's streets are much safer than they were in the 1950s, when Japan was poor, desperate and recovering from the trauma of the second World War, says Prof Yoji Morita, an expert on crime at Osaka Municipal University.

But this new wave of youth crime is causing deep unease. The attackers offer bizarre reasons for their behaviour. Earlier this year, a popular and academically gifted 17-year-old in central Japan stabbed an elderly woman to death because, he told police, he wanted to know what it would be like to kill someone. He also reportedly told police that he chose an older person because he didn't want to kill someone with a future.

Last month, a 15-year-old with an apparent fetish for ladies' underwear was arrested for stabbing to death three members of a neighbouring family with whom he had been friendly because they accused him of stealing undergarments from their home.

In May, a 17-year-old boy, meticulous, intelligent and mentally unbalanced, hijacked a bus in Kyushu, southern Japan, killing one and injuring five. The boy said he felt betrayed by his parents, who he reckoned didn't pay him enough attention. Local newspapers recently reported a case where two young women kidnapped an acquaintance and tortured her for six days because she apparently bad-mouthed another friend.

The problem is providing a rare unanimity of coverage in the Japanese media. The racy weekly magazines, who thrive on sex, murder and gossip, along with the more staid broadsheets and serious broadcasters are handing over column inches and air time to sociologists, educators, politicians and others with an opinion on how teenagers in the world's number two economic superpower should be taught the difference between right and wrong.

A buzzword in the media analyses is kireru, to snap. Experts, unable to find a convenient explanation for this spate of savage unprovoked crimes, say that more and more young people are simply snapping.

But Jinsuke Kageyama, a criminologist professor at Tokyo Institute of Technology sees other more logical explanations. He points to increasing cases of infantile omnipotence. All children, he says, dream about being able to carry out superhuman acts, but part of their transition into adulthood means they must discard that yearning. However, children, particularly spoiled ones, may not want to come to terms with the move to adulthood and hang onto their infantile feelings into adolescence, he says. This creates difficulties which they seek to overcome by resorting to crime.

This can be compounded by what Prof Kageyama calls the empty self, apparently common in so-called post-industrial societies, where an individual seeks to bury his own sense of emptiness through the crime.

Mr Yoshiro Mori, who has betrayed a nostalgia for a militarist Japan since becoming prime minister in April, favours a return to the harsher education system of pre-war Japan. Another traditionalist, Tokyo governor Shintaro Ishihara, who believes adults have a right to scold children, is promoting his pet scheme called "revolution in the hearts and minds" of Tokyoites. According to Ishihara's revolution, adults should berate misbehaving children, including other people's, while youngsters should grant others the basic civility of a greeting.

Others want to revise the Juvenile Law, which defines under20s as minors. Apart from denying minors the right to vote or drink alcohol, the law says that, if they kill someone, they will be usually tried as a juvenile, thus avoiding the death penalty.

Rewriting the law has the support of many politicians and would go down well with the public, but Prof Morita is unsure a change would do any good. The crimes, he says, arise from everyday social problems, from family and education problems. Changing the law may not help.

If, as Prof Morita suggests, the problem is a wider societal one, Japan cannot afford to ignore the issue. The general absence of natural raw materials in Japan means the nation relies more than most on its human resources, Prof Kageyama points out. It has no choice but to look after its peoples' mental as well as physical health.

For the moment, however, the future looks bleak. Prof Kageyama predicts a 21st-century rise in seemingly motiveless crimes committed by those who, while not classified as mentally ill, suffer from ego sickness or personality disorders.