It is believed that the killers were Toshizo HIJIKATA, Keisuke YAMANAMI, Soji OKITA, Sanosuke HARADA from the Shieikanha group of Isami KONDO that were opposed to the Mito group of SERIZAWA.
刺客は芹沢の水戸派と対立していた近藤勇の試衛館派の土方歳三、山南敬助、沖田総司、原田左之助という説が有力である。