"With the execution, I feel that the opportunity to discover (why) has been lost", Moriyama said.
Police leave an Aum Shinrikyo compound in the small village of Kamikuishiki at the foot of Mount Fuji on March 28, 1995.
The top Japanese government spokesman confirmed Asahara's execution but wouldn't comment on the others.
The cult's most notorious crime was the release of sarin gas on Tokyo subways in 1995.
Aum members first released it in 1994 in the central Japanese city of Matsumoto, in a failed attack on three judges set to rule on the cult, nevertheless killing eight people and making hundreds ill. As trials of cult members began taking place, numerous crimes were confessed to by members, including the production of VX nerve gas, attempts to manufacture automatic weapons, kidnapping, chemical attacks, and the murder of people deemed to threaten the cult.
Japan's Justice Ministry announced the executions of Asahara, 63, and his followers.
Asahara, whose original name was Chizuo Matsumoto, founded Aum Shinrikyo, or Supreme Truth, in 1984. It staged a series of crimes including simultaneous attacks on Tokyo's subway in March 1995 using sarin gas, a nerve gas originally used by the Nazis.
Asahara and five of the six followers had been implicated in the subway attack.
The Japanese Tribunal has prosecuted about 190 cult members for the attacks and other related crimes, including the 1989 murder of lawyer Tsutsumi Sakamoto and his family, and passed six life sentences and 13 death sentences.
He was sentenced to death after a lengthy prosecution during which he regularly delivered rambling and incoherent monologues in English and Japanese. However, ultimately, the death penalty was given to Shoko Asahara and others high in the chain of this organization.
AUM Shinrikyo renamed itself Aleph in January 2000. Last year, a court ruled that the Aum Shinrikyo no longer posed a threat to the public.
Japan forgoes executing death row inmates if an accomplice is still on trial.
"As I also bear a heavy responsibility, I would like to apologize to the victims", he said, although adding, "I have left Aleph more than 10 years ago, and I don't have any special feelings (for Asahara)". The followers of the three groups total about 1,650 in Japan and about 460 in Russian Federation, while the groups hold more than 1 billion yen ($9 million) in assets, according to the agency. Asahara also preached apocalyptic prophesies, which were the genesis of the subway attack: He believed the end of the world was coming, and the attack was a way to prepare.The Asahi Shimbun/The Asahi Shimbun via Getty ImagesPRESS CONFERENCEShoko Asahara (center) at a press conference in October 25, 1990.