Prosecutors asked for the death penalty Monday for a former senior member of Aum Shinrikyo accused of releasing sarin in the deadly March 1995 Tokyo subway gas attack that killed 12 and injured thousands, and illegally manufacturing firearms.

Prosecutors said before the Tokyo District Court that Masato Yokoyama, 35, participated in every major act leading up to the attack, including plotting the crime and inspecting the scene beforehand, proving he actively took part in the attack on March 20, 1995.

"There is no other option but to demand capital punishment," said a prosecutor, calling his act "merciless and coldblooded."