The group, led by Shoko Asahara, had already carried out several assassinations and terrorist attacks using sarin, including the Matsumoto sarin attack nine months earlier. They had also produced several other nerve agents, including VX, and attempted to produce botulinum toxin and had perpetrated several failed acts of bioterrorism. Asahara had been made aware of a police raid scheduled for March 22 and had planned the Tokyo subway attack in order to hinder police investigations into the cult and perhaps spark the apocalypse they believed in. The leader also wanted to start a Third World War.
On Monday, 20 March 1995, five members of Aum Shinrikyo launched a chemical attack on the Tokyo subway (on lines that are part of the present-day Tokyo Metro), one of the world's busiest commuter transport systems, at the peak of the morning rush hour. The chemical agent used, liquid sarin, was contained in plastic bags which each team then wrapped in newspaper. Each perpetrator carried two packets totaling approximately 0.9 litres (30 US fl oz) of sarin, except Yasuo Hayashi, who carried three bags totalling approximately 1.3 litres (44 US fl oz) of sarin. Aum originally planned to spread the sarin as an aerosol but did not follow through with it. Sarin has an LD50 of 550 micrograms per kilogram (0.0039 gr/lb), corresponding to 38.5 milligrams (0.594 gr) for a 70-kilogram (150 lb) human; however, dispersal issues dramatically reduced its effectiveness.
Carrying their packets of sarin and umbrellas with sharpened tips, the perpetrators boarded their appointed trains. At prearranged stations, the sarin packets were dropped and punctured several times with the sharpened tip of the umbrella. Each perpetrator then got off the train and exited the station to meet his accomplice with a car. Leaving the punctured packets on the floor allowed the sarin to leak out into the train car and stations. This sarin affected passengers, subway workers, and those who came into contact with them. Sarin is the most volatile of the nerve agents, which means that it can quickly and easily evaporate from a liquid into a vapor and spread into the environment. People can be exposed to the vapor even if they do not come in contact with the liquid form of sarin. Because it evaporates so quickly, sarin presents an immediate but short-lived threat.
Hayashi eventually chose to use Akahata. Wearing a surgical mask commonly worn by the Japanese during cold and flu season, Hayashi boarded the first car of southwest-bound 07:48 Chiyoda Line train number A725K. As the train approached Shin-Ochanomizu Station, the central business district in Chiyoda, he punctured one of his two bags of sarin, leaving the other untouched, and exited the train at Shin-Ochanomizu.
The train proceeded down the line with the punctured bag of sarin leaking until 4 stops later at Kasumigaseki Station. There, the bags were removed and eventually disposed of by station attendants, of whom two died. The train continued on to the next station where it was completely stopped, evacuated and cleaned.
Two men, Ken'ichi Hirose and Koichi Kitamura, were assigned to release two sarin packets on the westbound Marunouchi Line destined for Ogikubo Station. The pair left Aum headquarters in Shibuya at 6:00 am and drove to Yotsuya Station. There Hirose boarded a westbound Marunouchi Line train, then changed to a northbound JR East Saikyō Line train at Shinjuku Station and got off at Ikebukuro Station. He then bought a sports tabloid to wrap the sarin packets in and boarded the second car of Marunouchi Line train A777.
As he was about to release the sarin, Hirose believed the loud noises caused by the newspaper-wrapped packets had caught the attention of a schoolgirl. To avoid further suspicion, he got off the train at either Myogadani or Korakuen Station and moved to the third car instead of the second.
As the train approached Ochanomizu Station, Hirose dropped the newspapers to the floor, repeated an Aum mantra and punctured both sarin packets with so much force that he bent the tip of his sharpened umbrella. Both packets were successfully broken, and all 900 millilitres (30 US fl oz) of sarin was released onto the floor of the train. Hirose then departed the train at Ochanomizu and left via Kitamura's car waiting outside the station. Hirose's clumsy release of the sarin resulted in him accidentally poisoning himself, but he was able to administer an antidote stored in Kitamura's car.
At Nakano-sakaue Station, 19 stops later, two severely injured passengers were carried out of the train car, while station attendant Sumio Nishimura removed the sarin packets (one of these two passengers was the only fatality from this attack). The train continued with sarin still on the floor of the third car. Five stops later, at 8:38 am, the train reached Ogikubo Station, the end of the Marunouchi Line, all while passengers continued to board the train. The train continued eastbound until it was finally taken out of service at Shin-Kōenji Station two stops later. The entire ordeal resulted in one passenger's death with 358 being seriously injured.
Masato Yokoyama and his driver Kiyotaka Tonozaki were assigned to release sarin on the Ikebukuro-bound Marunouchi Line. On the way to Shinjuku Station, Tonozaki stopped to allow Yokoyama to buy a copy of Nihon Keizai Shimbun, to wrap the two sarin packets. When they arrived at the station, Yokoyama put on a wig and fake glasses and boarded the fifth car of the Ikebukuro-bound 07:39 Marunouchi Line train number B801. As the train approached Yotsuya Station, Yokoyama began poking at the sarin packets. When the train reached the next station, he fled the scene with Tonozaki, leaving the sarin packets on the train car. The packets were not fully punctured. During his drop, Yokoyama left one packet fully intact, while the other packet was only punctured once (and with a small hole), resulting in the sarin being released relatively slowly.
The train reached the end of the line, Ikebukuro, at 8:30 am where it would head back in the opposite direction. Before it departed the train was evacuated and searched, but the searchers failed to discover the sarin packets. The train departed Ikebukuro Station at 8:32 am as the Shinjuku-bound A801. Passengers soon became ill and alerted station attendants of the sarin-soaked newspapers at Kōrakuen Station. One station later, at Hongō-sanchōme, staff removed the sarin packets and mopped the floor, but the train continued on to Shinjuku. After arriving at 9:09 am, the train once again began to make its way back to Ikebukuro as the B901. The train was finally put out of service at Kokkai-gijidō-mae Station in Chiyoda at 9:27 am, one hour and forty minutes after Yokoyama punctured the sarin packet. The attack resulted in no fatalities, but over 200 people were left in serious condition.
The pair, with Takahashi driving, left Aum headquarters in Shibuya at 6:30 am. After purchasing a copy of Hochi Shimbun and wrapping his two sarin packets, Toyoda arrived at Naka-Meguro Station where he boarded the first car of northeast-bound 07:59 Hibiya Line train number B711T. Sitting close to the door, he set the sarin packets on the floor. When the train arrived at the next station, Ebisu, Toyoda punctured both packets and got off the train. He was on the train for a total of two minutes, by far the quickest sarin drop out of the five attacks that day.
Two stops later, at Roppongi Station, passengers in the train's first car began to feel the effects of the sarin and began to open the windows. By Kamiyacho Station, the next stop, the passengers in the car had begun panicking. The first car was evacuated and several passengers were immediately taken to a hospital. Still, with the first car empty, the train continued down the line for one more stop until it was completely evacuated at Kasumigaseki Station. This attack killed one person and seriously injured 532 others.
Yasuo Hayashi and Shigeo Sugimoto were the team assigned to drop sarin on the southwest-bound Hibiya Line departing Kita-Senju Station for Naka-Meguro Station. Unlike the rest of the attackers, Hayashi carried three sarin packets onto the train instead of two. Prior to the attack, Hayashi asked to carry a flawed leftover packet in addition to the two others in an apparent bid to allay suspicions and prove his loyalty to the group.
After Sugimoto escorted him to Ueno Station, Hayashi boarded the third car of southwest-bound 07:43 Hibiya Line train number A720S and dropped his sarin packets to the floor. Two stops later, at Akihabara Station, he punctured two of the three packets, left the train, and arrived back at Aum headquarters with Sugimoto by 8:30 am. Hayashi made the most punctures of any of the perpetrators. By the next stop, passengers in the third car began to feel the effects of the sarin. Noticing the large, liquid-soaked package on the floor and assuming it was the culprit, one passenger kicked the sarin packets out of the train and onto Kodenmachō Station's subway platform. Four people in the station died as a result.
A puddle of sarin remained on the floor of the passenger car as the train continued to the next station. At 8:10 am, after the train pulled out of Hatchōbori Station, a passenger in the third car pressed the emergency stop button. The train was in a tunnel at the time, and was forced to proceed to Tsukiji Station, where passengers stumbled out and collapsed on the station's platform and the train was taken out of service.
Hayashi later reported to the Japanese police investigators about the sarin attacks and Aum activities post-Tokyo subway attack; his cooperation with the authorities resulted in numerous arrests and convictions, and he was given a life sentence instead of death penalty. Tomomitsu Niimi, who was his getaway driver, was sentenced to death due to his involvement in other cri