https://motherboard.vice.com/en_us/article/gy3xex/what-is-aum-shinrikyo-sarin-attack

On March 20, 1995, two physicists, an artificial intelligence researcher, an engineer, and a heart doctor entered the Tokyo subway system at the peak of morning rush hour. Each of the men carried two small plastic bags wrapped in newspaper and an umbrella with a sharpened tip. After boarding five different trains, the scientists dropped the plastic bags at preordained stations and punctured them with the tips of their umbrellas before exiting the subway to rendezvous with their getaway drivers. As these scientists were whisked away to a hideout, the deadly sarin gas contained in their packages began to permeate the air in the subway tunnels.

By the time the air had cleared, 12 subway commuters were dead and over 1,000 others were injured through exposure to the potent nerve gas. It remains the deadliest act of domestic terrorism in Japanese history.