In autumn of the same year, he had patrolled Kyoto almost every day in a small group, and on September 30, when he encountered Kosaburo AKAMATSU, who was a scholar of military sciences supporting the idea of uniting the court and the shogunate, and engaged in military training for the army in the Satsuma clan, he assassinated him in the daytime as a spy of the shogunate.
同年秋、ほぼ毎日のように数人で京都見回りをしていたが、9月3日、薩摩藩で陸軍教練をしていた公武合体派の軍学者赤松小三郎と京都市中で遭遇し、幕府の密偵として白昼暗殺した。