During the Tokyo sarin gas attack, Ikuo Hayashi and Tomomitsu Niimi were involved in delivering the sarin containers on the Chiyoda line as a part of the Tokyo sarin attacks. Niimi served as the driver. Hayashi, wearing a surgical mask of the type commonly worn by Japanese during cold and flu season, boarded the southwestbound 7:48 a.m. Chiyoda line train number A725K on the first car. He was about to puncture the sarin packs but had second thoughts due to seeing dozens of commuters and fearing that releasing the sarin would endanger their lives, he also thought of aborting the attack.