From the material evidence such as the scabbard left on the scene at the time of Ryoma's assassination, and the testimony by Goryo eji including Kashitaro ITO assassinated three days later than Ryoma's assassination, Shinsengumi's Sanosuke HARADA was believed to be the Ryoma's assassin, but there is a theory that the sword wounds were by left-handed person.
龍馬暗殺当時の現場に残された鞘などの物証や、３日後に暗殺された伊東甲子太郎の御陵衛士らの証言から新選組の原田左之助によるものと信じられていたが、刀傷は左利きによるものであると言う説もある。