In 1867, Ito Kashitaro, a senior officer of the Shinsengumi broke off from the famous Kyoto Bakufu police force to form his own organization called The Guardians of the Imperial Tomb. This group withdrew to operate out of Gessin-In in southern Higashiyama. This new group was Imperialist in opposition to the Shinsengumi, and for their defection, they were hunted down and killed by the remaining Shinsengumi.
The exact details of the betrayal and the executions are unknown, however it is speculated that Saito Hajime, a captain of the Shinsengumi charged with routing out spies, was sent to infiltrate The Guardians of the Imperial Tomb. This however may be a conflation of his duties to ferret out spies within the Shinsengumi. Whether or not he was charged with spying on traitors is not within credible historical records.
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