Members of the cult, who are being held on a variety of unrelated charges, have admitted involvement in the killings, according to a report in today's Yomiuri newspaper.
An unnamed Aum member in his 40s has told police a group of cultists launched the attack from a base in Shibuya, in western Tokyo. On 19 March they threw a petrol bomb at the nearby Aum headquarters, apparently to mislead police by suggesting the cult itself was under attack. Shortly before 8am the next day, they released the gas simultaneously on five separate subway carriages.
The group was reportedly led by Yoshihiro Imoue, the cult's "intelligence minister", who is still at large. His notebooks, found by police, indicate that he visited the three lines attacked, noting train frequency and passenger numbers.
The cult has been under investigation since 22 March, but this is the first time individual members have been directly linked with the attack. Over seven weeks, hundreds of tons of chemical and biological ingredients, as well as gun parts, have been seized from cult premises. Aum spokesmen insist the substances were for making fertilisers and insecticides.
But last week another arrested member, Masami Tsuchiya, is said to have admitted to police that he synthesised sarin in a laboratory in the village of Kamiku Isshiki, near Mount Fuji. By-products of the gas have been detected around the laboratory complex.
On the basis of the confessions, police will apply for arrest warrants for Aum members, including Mr Asahara, the cult guru not seen in public since before the sarin attack.
Several Japanese papers have reported that police know his whereabouts and have him under observation. The most popular theory is that he is hiding in the Kamiku Isshiki complex, where an army of journalists and television crews have been camped for weeks awaiting "X-day", the moment when he emerges or is taken into custody.
The great fear is that cult members in hiding may have further sarin supplies. Sixty thousand extra officers were deployed throughout Japan this weekend in apparent anticipation of police action, and tension was heightened by a bomb explosion on Saturday at Narita airport, Tokyo, though there is no indication so far that this had anything to do with the cult.
Police were stationed around government offices and the parliament building yesterday, and a bomb disposal robot was in the district. Weekend patrols in railway and subway stations removed litter bins and put up notices explaining the measures were to protect the public.
The number of stories filtering through the Japanese media from police sources has increased in the past few days, suggesting the investigation may be entering its final stage.
Arrested Aum members have allegedly admitted illegal drugs were made in the cult's laboratories, both for brainwashing followers and to sell through the Yamaguchi-gumi, one of Japan's biggest criminal syndicates.
Suspicions that the cult has links with organised crime were reinforced when a member of the Yamaguchi-gumi was arrested in connection with the murder of Hideo Murai, a senior chemist in the sect who was stabbed to death in front of Aum's Tokyo headquarters.
It has been reported that, in the ambulance taking him to hospital, Murai muttered the word "Judas", leading to speculation that his death may have been planned by sect elements.