The execution of Japanese doomsday cult leader Shoko Asahara leaves unanswered questions about Aum Shinrikyo, the group behind the 1995 sarin-gas attack on the Tokyo subway that killed 13 people and sickened 6,000.
Japanese government spokesman Yoshihide Suga confirmed that Asahara was executed on Friday.
The authorities said six other cult members were hanged.
Born Chizuo Matsumoto in 1955, Asahara founded Aum Shinrikyo, or Supreme Truth, in the mid-1980s. It attracted young people disillusioned with the modern materialistic way of life.
Half-blind, with a shaggy hair and beard, Asahara was the key figure in the stunningly random and lethal attack targeting Tokyo commuters.
He used a mixture of Hinduism, Buddhism, Christianity and yoga to draw followers. They took part in bizarre rituals, such as drinking his bath water and wearing electrical caps they believed synchronised their brain waves with Asahara's.
Asahara chose doctors, lawyers and scientists from Japan's top universities as his top aides, making them ministers of his pseudo-government of the Aum empire.
They worshipped him and carried out his orders. The group used donations from followers and earnings from yoga classes and health food businesses to amass cash to buy land and equipment. They made and bought conventional weapons in and outside Japan, while the scientists he had recruited developed and manufactured sarin, VX and other deadly chemical and biological weapons.
During his trial, Asahara often used diapers and sat on a cushion intended to make his incontinence inconspicuous. He stopped communicating with his children and defense team.
A court-appointed psychiatrist suggested he might be faking insanity to avoid punishment.
The initial death sentence in 2004 became final after his defense team could not file an appeal citing his mental state.
In a rare interview in 2006, two of Asahara's four daughters told The Associated Press that never in dozens of visits to him in prison had they had a real conversation.
Asahara just sat and at times fidgeted or grunted. The daughters' repeated petitions for retrials were refused. They said his condition might have worsened since the last being allowed to see him in 2008.
Yoshihiro Yasuda, Asahara's main lawyer during his trial, said the last time he was allowed to see Asahara at the detention center was in 2006. After that, the Tokyo detention centre rejected requests for meetings with Asahara more than 400 times, citing the absence of a reaction from Asahara.
Yasuda sought medical treatment for Asahara and said in April 2018 that he had appealed for his release.
The reasons behind the sarin gas attack remain an enigma. Cult members have said they believed Asahara's prophesy that an apocalypse was coming and they alone would survive it.
Even before the attack, in 1989, lawyer Tsutsumi Sakamoto, who opposed the cult, his wife and baby boy were murdered by cult members.
Tomomasa Nakagawa, a doctor also executed Friday, and several other cultists broke into the Sakamotos' apartment late at night, strangled them to death and buried them in the mountains.
Cult activities escalated after the defeat of Aum members in the 1990 parliamentary election. During their bizarre election campaign, Asahara and his top disciples sang and danced to the guru's songs.
In June 1994, the cult spread sarin gas in Matsumoto in central Japan, killing eight people and injuring more than 140 others, in an attack targeting residents who were protesting the cult's presence in their neighborhood and court officials handling their legal disputes.
Nakagawa and key members produced sarin at a cult compound and sprayed it from a van, in what was later regarded as an experiment for the subsequent subway gassing. Under intensifying scrutiny from the government, the cult plotted the larger sarin attack on the subways in Tokyo on March 20, 1995.
Asahara guided the attack, according to testimony by his right-hand man, Yoshihiro Inoue, who also was executed Friday. Inoue headed Aum's intelligence unit and was one of the few cult members who later turned against Asahara.
The five cultists who carried bags of sarin onto the trains targeted three subway lines converging at Kasumigaseki, Japan's government and political center similar equivalent to Washington's Capitol Hill.
The horrifying scenes in the aftermath of the attack shocked a country where the crime rate is relatively low and people tend to take their personal safety for granted.
The investigation into the attack uncovered more doomsday preparations, weapons arsenals and multiple killings by Aum.
Asahara was captured two months later, dragged out of a hidden compartment in a ceiling where he had holed up to evade arrest.
In 2004, he was convicted of having killed 27 people in 13 murders and other assaults and kidnappings spanning six years that culminated in the subway attack in his elaborate scheme to hasten Armageddon that he threatened.