What drove a quiet, elderly man, to douse himself with fuel and set fire to it in a packed carriage on a speeding train?
As he tipped the liquid over himself he is reported to have shooed away other passengers, telling them it was dangerous.
Now, as they start to dig in to his background, members of the Japanese media are turning up the tell-tale signs of a man on the edge. He lived alone and had no job. He spent his days collecting aluminium cans to sell for recycling.
Neighbours told reporters they had heard him smash a window after locking himself out of his dilapidated apartment.
Others said they rarely saw him outside, but could often hear the sound of a television playing. Poor, old and alone. It is an all too familiar tale.
"Isolation is the number one precursor for depression and suicide," says Wataru Nishida, a psychologist at Tokyo's Temple University.
"Now it's more and more common to read stories about old people dying alone in their apartments," he says. "They are being neglected. Kids used to take care of their parents in old age in Japan, but not any more."
People often cite Japan's long tradition of "honourable suicide" as a reason for the high rate here.
They point to the Samurai practice of committing "seppuku" or to the young "kamikaze" pilots of 1945, to show there are distinct cultural reasons why Japanese are more likely to take their own lives.
To an extent Mr Nishida agrees.
"Japan has no history of Christianity," he says "so here suicide is not a sin. In fact, some look at it as a way of taking responsibility."
Ken Joseph from the Japan Helpline agrees. He says their experience over the last 40 years shows that elderly people who are in financial trouble may see suicide as a way out of their problems.
"The insurance system in Japan is very lax when it comes to paying out for suicide," he says.
"So when all else fails - some people feel - you can just kill yourself and the insurance will pay out.
"There is sometimes an intolerable pressure on the elderly that the most loving thing they can do is take their lives and thereby provide for their family."
Because of this, some experts think Japan's suicide rate is actually much higher than reported.
A lot of lone deaths of elderly people are never fully investigated by the police.
According to Ken Joseph, the almost universal practice of cremating bodies here also means that any evidence is quickly destroyed.
But it is not only elderly men in financial trouble who are taking their own lives.
The fastest growing suicide demographic is young men. It is now the single biggest killer of men in Japan aged 20-44.
And the evidence suggests these young people are killing themselves because they have lost hope and are incapable of seeking help.
The numbers first began to rise after the Asian financial crisis in 1998. They climbed again after the 2008 worldwide financial crisis.
Experts think those rises are directly linked to the increase in "precarious employment", the practice of employing young people on short-term contracts.
Japan was once known as the land of lifetime employment.
But while many older people still enjoy job security and generous benefits, nearly 40% of young people in Japan are unable to find stable jobs.
Financial anxiety and insecurity are compounded by Japan's culture of not complaining.
"There are not many ways to express anger or frustration in Japan," says Mr Nishida.
"This is a rule-oriented society. Young people are moulded to fit in to a very small box. They have no way to express their true feelings.
"If they feel under pressure from their boss and get depressed, some feel the only way out is to die."
Technology may be making things worse, increasing young people's isolation. Japan is famous for a condition called hikikomori, a type of acute social withdrawal.
The Japanese Ministry of Health, Labour and Welfare defines hikikomori as people who refuse to leave their house and isolate themselves from society in their homes for a period exceeding six months
According to government figures released in 2010, there are 700,000 individuals living as hikikomori with an average age of 31
An overlapping group of people with the hikikomori, otaku are "geeks" or "nerds"
While hikikomori is mostly a Japanese phenomenon, cases have been found in the United States, Oman, Spain, Italy, South Korea and France
The young person affected may completely shut himself - it is most often a male - off from the outside world, withdrawing in to a room and not coming out for months or even years.
But that is only the most extreme form of what is now a widespread loss of direct face-to-face socialising.
A recent survey of young Japanese people's attitudes to relationships and sex turned up some extraordinary results. Published in January by the Japan Family Planning Association, it found that 20% of men aged 25-29 had little or no interest in having a sexual relationship.
Wataru Nishida points to the internet and the pervasive influence of online pornography.
"Young people in Japan have a lot of knowledge," Mr Nishida says, "But they have no life experience. They have no idea how to express their emotions.
"They have forgotten what it's like to touch a person. When they think about sex they have high anxiety and no idea how to deal with it."
And when young people do find themselves isolated and depressed, they have few places to turn to.
Mental illness is still very much a taboo here. There is little popular understanding of depression. Those suffering its symptoms are often too scared to talk about it.
Japan's mental healthcare system is also a mess.
There is an acute shortage of psychiatrists. There is also no tradition of psychiatrists working together with clinical psychologists.
People suffering from mental illness may be prescribed powerful psychotropic medicines but unlike in the West, this will often not be accompanied by a recommendation that the patient seek counselling.
The counselling industry itself is a free-for-all.
Unlike in America or Europe, there is no government-mandated system of training and qualifying clinical psychologists.
Anybody can set him or herself up as a "counsellor" and it's very hard for someone seeking help to know whether they actually know what they are doing.
It is not a happy picture, and while the suicide rate has actually begun to decline in the last three years, it is still woefully high.
Wataru Nishida says Japan needs to start talking about mental illness much more, and not just as something scary and strange that afflicts a few.
"When you see a television discussion on mental illness in Japan they still talk as if 'depression equals suicide'," he says. "That needs to change."