Doomsday cult leader Shoko Asahara, the mastermind of a deadly sarin gas attack on the Tokyo subway, has been executed.

Japanese government spokesman Yoshihide Suga confirmed that Asahara, leader of Aum Shinrikyo, was killed along with six other cult members.

Aum Shinrikyo were responsible for the 1995 attack which killed 13 and injured thousands, with the executions leaving unanswered questions about the group.

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.

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 neighbourhood 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 on 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 centre.

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.

Born Chizuo Matsumoto in 1955, Asahara founded Aum Shinrikyo, or Supreme Truth, in the mid-1980s and it attracted young people disillusioned with the modern materialistic way of life.

With his shaggy hair and beard, the half-blind 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 bathwater 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.

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.

The initial death sentence in 2004 became final after his defence team could not file an appeal citing his mental state.

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