March 20th 1995, only 3 months after the devastating Kobe earthquake, 5 members of the Aum Shinrikyo cult released sarin nerve agent at locations all over the packed Tokyo subway system, at the peak of morning rush hour. Although only a tiny drop of sarin is needed to kill an adult, the sarin released on the subway was very slow to evaporate, and only 12 people were killed as a result. However, many thousands were injured and still suffer its effects even today.
Sarin gas attack on the Tokyo subway - Wikipedia