Japan's Supreme Court has rejected a final appeal by Aum Shinrikyo cult leader Shoko Asahara, paving the way for his execution, local media said.
Asahara's trial took eight years
Asahara was convicted in 2004 of masterminding a 1995 attack to release sarin nerve gas on the Tokyo subway during the morning rush-hour.
Twelve people died and hundreds more were injured in the attack.
Lawyers had appealed on the grounds that Asahara was mentally ill, asking for the case to be suspended.
The cult leader, a former acupuncturist, was sentenced to death in February 2004 after a trial lasting eight years.
He was also found guilty of other charges including plotting a 1994 gas attack in the central Japanese city of Matsumoto that killed seven people.
During his trial, he mumbled incoherently and made unexplained gestures.
1955 - Born in Yatsushiro, real name Chizuo Matsumoto
1987 - Starts Aum Shinrikyo
1994 - First sarin attack
1995 - Tokyo subway attack
1996 - Goes on trial
2004 - Trial ends
His lawyers say he has become mentally ill as a result of his detention and have tried to have legal proceedings against him suspended.
But in March a Tokyo court rejected an appeal, filed on mental health grounds, after Asahara's lawyers missed an application deadline.
This most recent action, a special motion, had challenged the March decision.
"Effective today, the court dismisses the special appeal of this case," a Supreme Court spokeswoman said.
Local media said that the final appeal avenue against Asahara's sentence, execution by hanging, was now closed.
Altogether, 12 cult members have been sentenced to death, but none of the sentences have yet been carried out.
Last month, a court upheld the death sentence for the cult's alleged second in command, a chemist who oversaw the development of the nerve gas.
Before the attacks, Aum Shinrikyo had thousands of members, many of them educated and wealthy, who embraced Asahara's violent apocalyptic teachings.
The cult changed its name to Aleph in 2000 and has renounced violence, but is still heavily monitored by police.