The cult leader Shoko Asahara, whose real name is Chizuo Matsumoto, had been in prison for 22 years before his execution this week. The attack left more than a dozen people dead and thousands wounded.
Twelve other Aum Shinrikyo members were sentenced to death for their roles in the Tokyo attack. Asahara's death sentence was finalized in 2006, according to the public broadcaster NHK, but the trials of his conspirators continued for another 12 years.
Since those proceedings ended earlier this year, the days of Aum Shinrikyo's members had been numbered, even when opponents of the death penalty tried to block executions.
Asahara was one of the seven members of the cult hanged this week. The others are Tomomasa Nakagawa, Tomomitsu Niimi, Kiyohide Hayakawa, Yoshihiro Inoue, Seiichi Endo and Masami Tsuchiya, according to Japanese Justice Minister Yoko Kawakami.
Six more people are still sentenced to die in connection with the 1995 attack and other Aum Shinrikyo crimes. The date of their executions is unknown.
Shizue Takahashi, representative of the group of victims and widow of an employee of Toyko Metro who died in the attack with sarin, told reporters that she was "surprised" by the sudden execution.
"When I think of those who died because of them, it was a shame (my husband's parents) and my parents could not hear the news of this execution," he said. "I wanted (the members of the sect) to confess more about the incident, so it's a pity that we can no longer hear your account."
In a statement on Friday, Amnesty said the execution of Asahara and other members of Aum Shinrikyo would not do justice to the Tokyo attack.
"The attacks perpetrated by Aum were despicable and the perpetrators deserve to be punished, but the death penalty is never the answer," said Hiroka Shoji, Amnesty International's East Asia researcher.
"Justice demands responsibility, but also respect for the human rights of all, the death penalty can never fulfill this as it is the maximum denial of human rights."
Beliefs of Judgment Day
Many of Asahara's followers were highly educated scientists and engineers, who helped to contribute large amounts of money to the sect's chests.
As the cult grew, the families of the members began to raise the alarm, and complaints of brainwashing and abuse within Aum Shinrikyo became more common.
Despite this, few would have predicted what was to come, and the cult jumped to world fame with the March 1995 attack on the Tokyo subway, when members of Aum Shinrikyo threw sarin gas in full carriages of passengers during rush hour. The attack killed 13 people and wounded 5,500.
Asahara and dozens of his followers were arrested in the following months, after police raids across the country.
Prosecutors said the cult members entered Sakamoto's house while they were sleeping, injected them with lethal doses of potassium chloride and strangled them.
The murder of Sakamoto and the growing clamor of members of the sect families caused more attention from the authorities, and Aum Shinrikyo began to prepare for the end.
Five members of Aum Shinrikyo boarded subway cars on three different lines in downtown Tokyo during rush hour, carrying plastic bags filled with sarin. They punched the bags with the sharp tips of their umbrellas and left them in the luggage racks or on the floor to filter the deadly gas in the wagons.
The trains had to arrive at the Kasumigaseki central station four minutes from each other, and the cult not only expected to kill everyone on board, but also to use the trains to deliver the gas to a massive exchange used by thousands of people. passengers at the same time
Fortunately, the mistakes made in developing sarin and its method of delivery meant that the attack was much less effective than anticipated, and the group only managed to kill 12 and injured 5,500 people. Another victim died later.
According to the FAS report, chemical weapons experts estimate that "tens of thousands could easily have died" if the attack had been carried out correctly.
Arrest and trial
Dozens of members of Aum Shinrikyo were arrested after months of police raids in hundreds of locations throughout Japan.
Asahara himself was arrested in May 1995 and charged with 17 counts ranging from murders to illegal production of weapons and drugs.
At the end of 1996, Ashara admitted responsibility for the sarin attack, but said he did not personally participate in the crime, saying he had been "instructed by God" to bear the guilt. At the same time, he warned lawyers that they would die if they continued to interrogate the members of Aum Shinrikyo.
After a trial that lasted eight years, Asahara was found guilty of planning the attack and sentenced to death in 2004. In 2006, he had exhausted the appeals process.
James Griffiths reported from Hong Kong, Yoko Wakatsuki reported from Tokyo