In March 1995, the world’s busiest subway system was brought to a standstill as a mysterious gas was released across the Tokyo underground.
Commuters in the Japanese capital began to feel short of breath and experienced dim vision. A dozen people died and thousands were affected.
It later transpired the deadly nerve gas sarin had been released in five locations across the network by the Aum Shinrikyo doomsday cult.
Toshiaki Toyoda was the deputy station master at Kasumigaseki station on that day.
He spoke to Witness about his experience and the guilt he feels at not being able to save his colleagues.