It’s great to see that even though the criminal is known, it doesn’t automatically end the case. Like Sakon said, you need solid proof. And that’s what this episode was about: getting the proof out of the culprit: Oki. Ayatsuri Sakon really knows how to play with human emotions and feelings. Sakon knew that if he mimicked the dead, and made them act the way he thought they would, Oki would suspect that they were onto him, and he would try to move the body as soon as he thought that everyone’s gone. This also played a major part in the first arc.
The reason for murder was a simple one: Oki was simply obsessed with Byakko. He wanted to have the sword, no matter what, and he killed Kyouichi when it appeared that the sword was going to be sold. He killed Akazuki because there had to be a time in which he had to find out that the sword didn’t end up on the black market. Though that reason confuses me a bit. After all, didn’t everyone think that Kyouichi took the blade and kept it as his own? If that’s the case, how would it end up in the black market of all places?