According to sources in the investigation, the attack was planned and carried out by a hand-picked group of between 10 and 20 cult members, led by 25-year-old Yoshihiro Inoue, the sect's "intelligence head" who was arrested in Tokyo early yesterday.
On 28 February, Inoue is believed to have kidnapped the brother of an escaped cult member who was refusing to give her money to the cult. On 1 March, members of the group rented an apartment in the Shibuya area of western Tokyo. This safe house was about a mile from the Aum headquarters in Minami-Aoyama, where police later found notebooks kept by Inoue, in which he recorded reconnaissance journeys around the Tokyo subway system. As well as the times of trains, he noted the volume of commuters at stations on the Hibiya, Chiyoda and Marunouchi lines, where the gas was later released.
On Sunday 19 March, Inoue accompanied a sergeant in the Japanese Self- Defence Forces, who threw a petrol bomb at the Minami-Aoyama building, apparently to give the impression that Aum was itself the victim of a terrorist attack.
The group then met at the safe house where the supplies of sarin gas were being stored. The sarin was made in the cult's laboratory at Kaniku Isshiki, 70 miles from Tokyo on the slopes of Mt Fuji, and stored in industrial nylon bags, which were specially made in the laboratory.
The machines have been found at Kamiku Isshiki; they produce a unique pattern on the seams of bags, which matches markings on the bags later found in the subway.
The bags were wrapped in early editions of the 20 March newspapers. About 6am that morning, the group left the house and divided into several teams carrying the sarin, which was planted on five trains on the three subway lines. All the trains were due to converge on Kasumigaseki station, the home of several government ministries and the National Police Agency.
Members kept watch on the trains while others punctured the bags of sarin at the height of the morning rush hour. Twelve commuters died and 5,500 others were treated for the effects of the gas. Two Aum members were hospitalised, but discharged themselves from hospital.
The next day, 21 March, local residents reported intense activity at Kamiku Isshiki: many cars and trucks left the commune, including the white Rolls-Royce used by the cult guru Shoko Asahara. On 22 March, the police began their raids.