On a sunny morning in March 1995, a secretive group called Aum Shinrikyo quietly released bags of liquefied sarin gas on the Tokyo underground. Twelve people were killed, thousands were made ill, and Japan's image as a bastion of safety was shattered.
By Sarah Buckley
BBC News Online
Nearly nine years later, Shoko Asahara, the leader of the group, is on Friday due to hear his verdict. Charged with masterminding a series of violent crimes, including two deadly nerve gas attacks, the partially blind guru faces the death penalty if found guilty.
What is less clear is the scale of the threat Aum, and some of the country's other quasi-religious groups, continue to pose to Japan.
Aum's new leader, Fumihiro Joyu, claims to have renounced violence
Mr Asahara set up a small religious sect in Tokyo in 1984 and renamed it Aum Shinrikyo in 1987. It espoused a mixture of Hindu and Buddhist beliefs and the writings of Nostradamus.
Members of the cult, who had not demonstrated violent tendencies before they joined Aum, were fed a diet of violent apocalyptic teachings.
"Most of them had very few rebellious periods in their teens... They were from good stable households and were normal kids," Taro Takimoto, a lawyer whose fight against Aum nearly lost him his life at the hands of the cult, told BBC News Online.
Ironically it seems likely their backgrounds made them more vulnerable to the charismatic Mr Asahara's power.
"Many of them were naive about the corrupted nature of some people in society... they joined Aum with the true belief that they were going to make the world a better place," Mr Takimoto said.
Andrew Marshall, co-author of The Cult at the End of the World: The Incredible Story of Aum, says they were arguably not helped by a "straight-jacketed" education system which does not nurture critical faculties.
Aum also offered practical spirituality in a society absorbed throughout the 1980s with economic development.
Although many Japanese claim to adhere to the nation's traditional religions of Buddhism and Shinto, their worship often seems to fulfil a cultural rather than emotional need, according to Ian Reader, a lecturer in religious studies at Lancaster University in the UK.
"They [Asahara's followers] were looking for something more spiritually nourishing," Mr Reader said.
Aum has since renamed itself Aleph and renounced violence.
Fumihiro Joyu, the group's new leader has said that while Mr Asahara is still considered a "genius of meditation" the group "cannot approve" of the activities conducted by Aum under his leadership and that he is no longer considered the group's guru.
"We will abandon the parts of [his] teachings that are considered dangerous," Mr Joyu has written on Aleph's website.
Last year, a group called Pana Wave caught the nation's attention
The Japanese government is not convinced.
"The threat that Aum poses today hasn't changed since the [sarin] attacks on Matsumoto and Tokyo," said a spokesman for Japan's Public Security Investigation Agency (PSIA).
"The Aum followers, they still maintain their absolute faith in Asahara and they maintain faith in his doctrine too," he said.
The PSIA said that it had not found any specific terror plans, or any signs that Aum was capable of producing sarin today, but that its beliefs, and the high standards of education and technical ability possessed by its members, meant it was still dangerous.
Its membership - which is thought to have numbered in the thousands at the time of the 1995 attack - has dropped to around 450, according to the PSIA, although the agency says it has shown signs of gradually increasing.
Mr Takimoto agrees that Aleph remains an unknown quantity, but that security has been improved.
"22 March 1995 was a major wake-up call. Japan has been through it. The police were lax until then but now things are much better," he said.
What has not changed are the factors that helped to nurture Aum, and the number of other quasi-spiritual groups in the country - the government has estimated there could be more than 200,000 cults at large.
Some, like Ho-no-hana Sampogyo, a so-called foot-cult led by "His Holiness" Hogen Fukunaga, seem to have no more than profit as their main motivation. Others could be more sinister.
The PSIA would not name the groups under its surveillance, but admitted that "after the '95 attacks, we are quite interested in keeping a close watch on related organisations".
Shoko Egawa, a Japanese journalist who has written several books on Aum, and who was nearly gassed to death herself by the group, said she did not believe that cults posed any greater threat to Japan than any other developed nation.
But she did say many Japanese may be missing the point by only viewing the cult problem as a matter for the police.
"What we Japanese lack might be studying our society from every angle ourselves," she said.