Violent crime rates in Japan are dropping and homicide rates are at all-time lows, but the mass killing last Tuesday by a 26-year-old influenced by Adolf Hitler has cast a harsh glare on murders committed by disaffected youth here.
A roll call of sordid crimes committed by youth under 35 over the decades may suggest a need for more timely counselling or even early psychiatric intervention for those identified to be at risk.
Yet this may be anathema in a Japan that is only slowly starting to open up to mental health issues. A 2013 study in the Psychiatry and Clinical Neurosciences journal said nearly two-thirds of those with mental illness do not seek help because of social stigma.
Even then, there are those who have had help but still slip through the cracks - like last Tuesday's alleged suspect Satoshi Uematsu, whose stabbing rampage at a Sagamihara home for the disabled was the deadliest in post-war Japan with 19 dead and 26 injured.
He had been deemed a threat to society and forcibly warded for 12 days in a mental hospital in February, but questions now prevail as to whether adequate aftercare was given to prevent the relapse.
Uematsu is not a "terrorist" in the usual sense, but in his hate crime he showed identical warning signs of the disenchanted youth elsewhere who have subscribed to radical ideologies, as a Nikkei editorial noted last week.
It described such persons as: "A lone-wolf actor, often resentful of his own position in society, crosses an ideological threshold and commits an act of violence."
Uematsu is said to have been dissatisfied with his job, believing that taxpayers' money should instead go to able-bodied persons in need.
He had also started taking drugs and keeping to himself - a drastic change from the earnest young man that some at an elementary school, where he was a trainee teacher, had described in local media.
Experts like Tokyo International University sociologist Thomas Blackwood stress that the incident is not indicative of a trend of violent youth crimes in Japan, which remain few and far between.
He tells The Straits Times: "In fact, the evidence seems to be pointing in the opposite direction. "Japanese elderly now commit more crimes than teenagers, and Japanese young people commit far fewer murders today than they did decades ago."
But even so, some of Japan's most heinous crimes have been committed by young people.
And perpetrators of extreme acts are typically "people with some axe to grind who are fluid - that is, they're truly at their core struggling with suicide and homicide, and they swing between the two", Dr J. Kevin Cameron, director of the Canadian Centre for Threat Assessment and Trauma Response, told The New York Times in a report last week. "Today, the person is more suicidal; a week later, he's more homicidal."
One such example is Tomohiro Kato, then 26, who killed seven and injured 10 others in the popular electronics belt Akihabara in 2008.
Two years earlier, he had attempted suicide by ramming his car into a wall, being deeply in debt and thinking his family had given up on him. Mired in poverty and sacked from his dead-end temporary job, he wanted to vent his pent-up anger.
"I'm lower than trash because at least the trash gets recycled," he had written on an Internet bulletin board where he also gave blow- by-blow updates of his attack.
The incident occurred some 20 years after Tsutomu Miyazaki, notoriously dubbed the "otaku murderer", killed four girls aged between four and seven and sexually molested their corpses.
Miyazaki, who was born with deformed hands and ostracised by society for his disability, was 26 at the time of his arrest.
Sociologist Emi Kataoka of Komazawa University in Tokyo said frustration with society or hopelessness over one's future are reasons youth might lash out in violent ways. "Japanese youth have been divided according to their economic conditions, values and attitude," she tells The Straits Times.
A weak economy means over 30 per cent of youth work as non-regular workers in Japan today, she says.
This, of course, does not mean all or even most of them are prone to violent crime, but a few could be pushed to the brink if coupled with other pressures like social discrimination or isolation.
There are also cases of murders committed by teenagers who could have been influenced by popular culture or copycat crimes.
Latest statistics by Japan's National Police Agency last Friday showed 60 such cases in 2015 by those aged between 14 and 19.
In February last year, three boys - two aged 17 and one aged 18 - brutally murdered a 13-year-old in Kawasaki in Kanagawa prefecture in a killing purportedly inspired by beheadings by the Islamic State in Iraq and Syria terror group.
A month earlier, a 19-year-old girl from Nagoya University was arrested for killing a 77-year-old woman. She told the police she "had wanted to kill someone since childhood", and it could have been "anybody".
In June this year, a 16-year-old boy killed a 42-year-old woman in a park in Iberaki prefecture, dumping her body in a lake after he "felt a sudden urge to do so".
The popularity of social media has also exacerbated another threat - stalking - that in some cases has led to violent crime.
In May, Tomohiro Iwazaki, 27, who had stalked pop idol Mayu Tomita, 20, by sending her multiple private messages on Twitter, stabbed her more than 20 times after he felt "humiliated" that she rejected his advances. She is recovering.
Dr Kataoka says last Tuesday's killing may prompt a review to "strengthen the systems to prevent terrible crimes and keep a close eye on youth at risk".
But the first step should be a deeper analyses of the root causes, rather than "excessively strengthening the control and surveillance", she says.