After a trial lasting eight years, the verdict will be handed down this week against Shoko Asahara, the self-styled guru who founded the Aum Supreme Truth cult behind the 1995 Tokyo subway nerve-gas attack.
Prosecutors have demanded the death sentence for the 48-year-old accused of masterminding the plot to release Nazi-developed Sarin gas into the Tokyo metro. Twelve people were killed and more than 5,000 injured in the attack.
The near-blind yoga-master, whose real name is Chizuo Matsumoto, has been charged with planning at least 13 crimes, which resulted in the deaths of a total of 27 people.
He is also charged with ordering cult disciples to be killed and for another Sarin attack in central Japan in June 1994 that left seven people dead.
Prosecutors have branded offenses on the charge sheet as "crimes of a devil who has lost his humanity completely," and have labelled the guru "the most atrocious criminal in our nation's history."
They called for the death sentence against Asahara last April, saying that "under the guise of religion, (he) ordered followers to commit crimes purely to satisfy his own greed for power."
Members of the cult, which was founded in 1984, have testified in court that the offences were committed under Asahara's orders. The cult has acknowledged responsibility for the crimes and apologised.
But Asahara's 12 court-appointed defense lawyers -- who are opposed to the death penalty in principle -- have argued that the cult leader is innocent and that his followers were out of control when they committed the crimes.
Eleven cult members have already been sentenced to death, but none has yet been executed, pending appeals.
The landmark judgment will be delivered on Friday at the Tokyo District Court where more than 12,000 people queued for a handful of seats open to the public on the first day of his marathon trial in April 1996.
Asahara was arrested two months after the 1995 attack at Aum's ramshackle headquarters in Kamikuishiki in the foothills of Mount Fuji, where the sect had built a chemical plant capable of producing enough Sarin to kill millions.
At the time of the attack, Aum boasted 10,000 followers with four overseas branches including Moscow and New York.
Asahara recruited and brainwashed brilliant misfit scientists to produce deadly chemical, biological and even nuclear weapons, prosecutors said.
In exchange for all their earthly possessions, Asahara promised the cult's rank and file a hand in making a new world after an Armageddon that was supposed to occur in 1997.
Asahara has said he found enlightenment in the Himalayas in 1986, and the sect revered Shiva, the Hindu god of destruction, although it was also heavily influenced by Buddhism.
The guru has refused to testify except for a few inconsistent remarks.
"I am responsible for these cases," he once told the court, but hours later he said: "I am totally innocent."
He also once demanded a halt to the spectacle of an "abnormal" and "ridiculous" trial, but said "I don't mind being hanged if you wish."
The cult itself escaped being outlawed under the Subversive Activities Prevention Act in 1997 when a legal panel ruled there was no reason to believe it could still pose a threat to society.
Aum has since renamed itself Aleph and deposed its founder, but police suspect his influence in the group remains high, saying some of the believers still use pictures of the guru and recordings of his voice in meditation.