The explosion occurred shortly after 7pm. Maskai Usumi, 44, an aide to the Governor, lost his left hand and right thumb after opening a large brown envelope.
"Suddenly there was the sound of a huge explosion, and he was lying on the ground with his fingers gone," a cleaner said. "Then there was just panic: clouds of smoke, and people screaming and coughing."
Mr Aoshima, who was in another part of the building at the time, is a controversial figure. He has a popular following but also many political enemies. He is a prize-winning writer and television comedian, whose election in April as an independent candidate upset political circles. His decision to cancel the Tokyo World City Expo, planned for next year, angered politicians and businesses that intended to invest in the project. Last week, he was heckled by conservative politicians in the Tokyo Metropolitan Assembly. It is hard to imagine, however, that Mr Aoshima's opponents would resort to terrorism.
Suspicion will inevitably focus on Aum Shinri Kyo, which hoarded hundreds of tons of chemical, biological and explosive ingredients in its buildings near Mt Fuji, close to where Mr Asahara was found yesterday.
Police arrested the cult leader in his residence in the village, more than four hours after breaking into the building with electric cutters.
The building had been searched by police several times during a seven- week investigation into the cult, but they did not know his whereabouts until recently. Electricity had been cut off, and investigators carrying torches had to force their way into the many small rooms. Mr Asahara was found in a one-metre-high compartment, concealed between the second and third floors. He was meditating alone in his purple robes and offered no resistance.
He was arrested on suspicion of the murder of 12 commuters and the attempted murder of 5,500 who were poisoned in the sarin subway attack on 20 March.
Mr Asahara was driven to the Tokyo Metropolitan Police (MPD) headquarters, 100km away. Under questioning the cult leader, who is visually impaired, denied the charges. "How could I, with my bad eyes, have done such a thing?" he asked. But, despite claims by his followers that he has been ill, Mr Asahara appeared in good health. When a doctor tried to take his pulse, he was brushed away. "I am fine," Mr Asahara said. "Don't touch me, please. I don't allow even my disciples to touch me."
Dawn raids were carried out on 130 other Aum facilities and by the end of the day about half of the 41 people named in the murder warrants were in custody. Still at large was Takeshi Matsumoto, a member of the sect's "Intelligence Ministry", suspected of kidnapping a cult member's brother in February.
The Japanese Prime Minister, Tomiichi Murayama, announced that the sect would be dissolved. But he warned: "They may have produced more sarin and are still concealing it. We need to stay on the alert."