TOKYO >> Thirteen Japanese cult members may be sent to the gallows any day now for a deadly 1995 gas attack on the Tokyo subway system and other crimes. But when is uncertain. Such is the secrecy that surrounds Japan’s death penalty system.

Tuesday marked 23 years since members of the Aum Shinrikyo cult punctured plastic bags to release sarin nerve gas inside subway cars, killing 13 people and sickening thousands. Cult leader Shoko Asahara and a dozen followers were sentenced to death for that and other crimes that killed 27 in all. Their sentences date back as far as 20 years.

Tuesday at 8 a.m. — around the time of the attack — uniformed subway employees lowered their heads in silence at Kasumigaseki station, a main target of the cult. Shizue Takahashi, the 71-year-old widow of an assistant stationmaster who died in the attack, and the current station master placed flowers on a temporary altar set up for offerings.

“It seems the (legal) process has entered a next stage,” Takahashi told reporters. “I hope (executions) are carried out in accordance with the law.”

The relocation of seven of the cult members to five detention centers outside of Tokyo last week has sparked speculation that executions could be imminent. In Japan, accomplices in a crime are customarily hanged on the same day. Ten of those on death row were convicted for the subway attack, a number beyond the Tokyo detention center’s daily capacity.

As with all executions in Japan, when and where they will be killed isn’t being released, even to family members and lawyers. The executions won’t be announced until they have already happened.

Takahashi recently asked the Justice Ministry for a chance to meet the convicts and witness their executions. “I want to follow through to the very end,” Takahashi said at a recent news conference.

Her wish is unlikely to be granted.

Even prisoners sent to the gallows are not notified until guards come to their cells in the morning. After a chat with a chaplain, a last bite or a smoke, the prisoner is taken to the gallows.

If all 10 subway attack convicts are hanged, it would be the second-largest number executed on a single day in Japan’s modern history. On Jan. 24, 1911, Japan hanged 11 political prisoners who allegedly plotted to assassinate the emperor.

Some survivors of the cult’s crimes oppose the executions because that would eliminate hopes for a fuller explanation of the crimes.

Asahara talked incoherently, occasionally babbling in broken English, during his eight-year trial and never acknowledged his responsibility or offered meaningful explanations.

Born Chizuo Matsumoto, he has been on death row for nearly 14 years. His family says he is a broken man, constantly wetting and soiling the floor in his cell and not communicating with his family or lawyers.

His 34-year-old daughter, Rika Matsumoto, said he doesn’t understand his punishment and needs treatment so he can recover and talk. “I just want to hear my father explain in his own words,” she tweeted recently.

Some of the condemned have expressed regret and contributed to anti-terrorism measures. Shoko Egawa, a journalist who has covered the cult’s crimes from early on, has proposed keeping them alive so they can provide lessons to a world facing the growing threat of extremism.

Experts on the cult also warn that if they are executed, the members would be glorified as martyrs by cult remnants, likely bolstering their worship of Asahara.

Founded in 1984, the group attracted many young people, even graduates of top universities, whom Asahara hand-picked as close aides.

The cult amassed an arsenal of chemical, biological and conventional weapons to carry out Asahara’s escalating criminal orders in anticipation of an apocalyptic showdown with the government.

The cult claimed 10,000 members in Japan and 30,000 in Russia. It has disbanded, though nearly 2,000 people follow its rituals in three splinter groups, monitored by authorities.