The 20-plus years of criminal trials involving members of the now-defunct doomsday cult Aum Shinrikyo came to a close Friday as the Supreme Court upheld the life sentence of Katsuya Takahashi, who was convicted of murder in the 1995 sarin attack on the Tokyo subway system.

The Aum trials were unprecedented in Japan’s judicial history in terms of their sheer number and the length of the deliberations. The focus now shifts to when the 13 members on death row — including Aum founder Shoko Asahara, 62, whose real name is Chizuo Matsumoto — will be hanged.

A series of terrorist attacks and other crimes committed by Aum resulted in the indictment of about 190 people. Due to the complexity of the background of the cases and the members’ relationships, the trials dragged on. Asahara’s trial, in particular, took seven years and 10 months, with the courts convening 257 times in total.

Exchanges involving insignificant details were often repeated. The families of the victims eventually grew critical of the defendants, saying they were using stalling tactics.

This criticism led to the enactment of a law aimed at forcing the courts to finish deliberating all cases within two years, and the introduction of pretrial arrangement procedures to let the judge, prosecution and defense meet in advance to clarify the points of contention and sort evidence before trials begin. In 2008, a system allowing crime victims to participate in trials was introduced, followed by the launch of the lay judge system the following year.

In December 2011, all of the Aum defendants — apart from Takahashi and two other members who were on the run — had their sentences finalized, making it appear as if the trials had finally ended.

Then, later the same month, member Makoto Hirata, 52, turned himself in to the Metropolitan Police Department. Fellow fugitives Naoko Kikuchi, 46, and Takahashi, 59, were arrested soon after, triggering the resumption of the Aum trials.

Some victims of Aum’s crimes say that, due to the new system allowing victims to be present in the courtrooms, they were given the chance to look squarely at the defendants and ask them questions directly, which made them feel the legal changes were worth the effort.

But Taro Takimoto, a lawyer who supported people who fled the cult, said the old system was more meaningful because it showed how the cult members were under the “mind control” of Asahara.

“Under the lay judge system, the scope of the trial has had to be narrowed down, exposing the limits of fact-finding,” Takimoto said.

It has been customary in Japan not to execute someone on death row if the case of an accomplice is pending before a court. Now that the last Aum member on trial has had his case closed, there is no barrier to execution. Any one of them could be hanged at any time.

According to a Justice Ministry source, there are essentially two options: to execute all 13 on the same day, or execute Asahara first.

The ministry is known for its tendency to postpone the execution of people with severe mental disease. While Asahara is rumored to be in poor health, a senior ministry official said the founder “is not in an abnormal state, both physically and mentally, and there’s no reason not to execute.”

Not a few ministry and prosecution sources have expressed anxiety over what will happen after the executions, saying they fear groups who have taken charge of Aum might seek revenge on the justice minister, who must sign off on each one. There are also other unresolved issues, such as who will deal with their bodies.

Public security officials say there is a possibility that Asahara could be deified by remnants of the cult. Three groups have taken over Aum — their ranks number 1,650 and they collectively have ¥1 billion in assets, the officials said.

“We cannot leave someone who committed such heinous crimes to die from disease,” a senior Justice Ministry official said.

Another official once involved in an execution said that carrying out Matsumoto’s death sentence has long been a priority at the ministry.

“Now we can finally resolve this important issue,” the official said.