As this has been an unsolved case, there are various theories about the possible murderers and the mastermind of the assassination; it is commonly thought that fuhei shizoku (former samurai with gripes) of the former bakufu (Japanese feudal government headed by a shogun) side, who felt uncomfortable with the restoration government, or the remnants of the former army of bakufu must have been the assassins and its mastermind.
未解決事件であるため、暗殺の下手人・黒幕に関しては諸説あるが、その怨恨的手口・新選組的手口から、維新政府を快く思わない旧幕府側の不平士族や旧幕府軍の残党が下手人・黒幕として一般的に考えられている。