He informed Kaoru about this last night and have told him to go all out against Tazuna, despite the sword being in its sheath, Kaoru's strength was enough to use his sword as if it was not in its sheath.
That is why from the very beginning both he and Kaoru had no desire to leave Tazuna intact. They knew that the people will feel bad for their acting chief if Kaoru would attack him to the point of no return but if they could exploit him while Kaoru was doing this then the people's heart would be moved by Kaoru's passionate revenge for the people.
True to their thoughts, upon reading the news and seeing their seals and signatures, the people was enraged to the point of them cheering Kaoru to end the bastard's life.
The people already had little trust for this person, after becoming the chief and leaving a few promises they never really saw him do anything. It was still the initiation of the people to improve their livelihood that helped the kingdom.
