A timeline of attacks in Japan:

March 20 - Sarin gas is released on five crowded Tokyo subway trains, killing 11 people and injuring more than 5,000. Police find specially sealed bags containing sarin residue.

March 22 - Police find hundreds of tons of chemicals in raids on Aum Shinri Kyo (Supreme Truth) doomsday cult.

April 13 - Unidentified Aum member warns in TV interview of impending disaster on scale greater than Kobe earthquake, which killed 5,500 people in January.

April 19 - Nearly 400 people are rushed to hospitals in Yokohama, Japan's second-largest city, after mysterious gas is released into railroad system.

April 27 - National Police Agency orders nationwide search for Aum's leader, Shoko Asahara.

May 6 - Guards thwart gas attack that could have killed 20,000 people in Shinjuku, Tokyo's largest station, defusing device in a washroom before it can release cyanide gas.

May 15 - Police capture suspected commander of subway attack, Yoshihiro Inoue.

May 16 - Police arrest Asahara inside a sect building.

May 26 - Aum is reported to have planned to arm followers with automatic weapons for guerrilla raids against parliament and prime minister's residence.

June 6 - Asahara and six other senior cult members are indicted on murder and attempted murder charges.

July 4 - Device that could release enough cyanide gas to kill 9,000 is found in Tokyo's Kayabacho subway station.

July 5 - Three people are overcome by fumes at Shinjuku railroad station, and police find mysterious liquid in men's room. Strange device is found at Ginza subway station in heart of Tokyo's most fashionable shopping district.