东京地铁毒气事件20周年 日本各界悼念死者

Friday marks the 20th anniversary of a nerve gas attack in the Tokyo subway by an apocalyptic cult, Aum Supreme Truth.  Thirteen people died and more than 6,000 people were injured.

On Wednesday, for the first time ever, the Japanese police authority released the audio recording of the communication between police when the attack happened.

This is the first alert of the atrocity by the Aum Supreme Truth cultists. And in the coming hour, calls for help and emergency reports would flood in, as chaos overtook the Tokyo subway system.

The liquid was sarin nerve gas.  Five cult members had brought it on the trains during rush hour, puncturing the packages with sharpened umbrella tips.

Sarin is so toxic that a single drop can kill a person.  It was being released into the air as thousands of unsuspecting commuters got on and off the trains.

And within an hour, 13 people were dead and more than 6000 injured. But investigators later found, it was just the beginning of a conspiracy.

"The Aum Supreme Truth cult planned to produce tons of sarin and disperse it in downtown Tokyo. If they had succeeded, we cannot imagine its consequence," said Keizo Fukufuji, former Japanese Police researcher.

Thirteen Aum members, including its leader Shoko Asahara, are on death row. The murder trial of the final suspect, Katsuya Takahashi, began in January after his arrest in 2012.  But public concerns over the sarin attack are far from over.

Two decades later, Japan remains largely baffled by why the cultists -- including scientists and doctors who had graduated from the country's top universities -- launched the attack.

And the world is worrying that the nerve gas, which is so fatal and easily produced, could bring more harm in the hands of extremists.