Based on the testimony given by a former Mimawarigumi member Nobuo IMAI, it is alleged that Sasaki assassinated Ryoma SAKAMOTO and Shintaro NAKAOKA of the Tosa clan at Omiya in Kyoto in 1867 (the Omiya Incident).
元見廻組隊士今井信郎の証言から、慶応3年（1867年）の京都近江屋での土佐藩の坂本龍馬・中岡慎太郎を暗殺したとされる（近江屋事件）。