As Kinzo revealed there is no inheritance, Kanon’s face was striken with absolute horror.
Why would that be? It is not as though Kanon had any chances of getting the inheritance for himself. Furthermore, he does not seem to be the type to care that much for material wealth. So, why the horrified reaction? I’ve reflected on this for a while, and only a single good answer comes to me.
He realized he killed a man for nothing.
Why would Kanon kill Rudolf, and how would this have anything to do with the inheritance? The answer would be love, of course. Kanon did not have grand dreams for himself, but he loved Jessica. Even if he might have no wishes for himself, he would wish for the safety of Jessica. In this case, financial safety. The battle over the inheritance made Rosa, Eva and Rudolf threats to Krauss’ claim to the inheritance, and by extension, Jessica’s future. For Jessica’s safety to be guaranteed, the battle for the inheritance would have to be resolved in Krauss’ favour. And Kanon could do nothing about it… except eliminate his rivals.
I know this game is only about the how, and thus it is superfluous to write this in blue, but I’ll do it anyway. It was Kanon who killed Rudolf, and it was for the sake of Jessica’s future.
Then, the question becomes “how could Kanon kill Rudolf between 11 PM and midnight?”. It has been confirmed in red that Kanon couldn’t have murdered Rudolf between 11:40 and 11:53. He was with the cousins from 11:53 onwards. Until 11:10, his hand was being fixed up and from 11:15 to 11:40, he was in Kinzo’s study. So, that leaves 11:10 to 11:15 as the only gap in narration during which Kanon was unsupervised. Kanon shot Rudolf to death during this brief interval between him leaving Nanjo’s care and him arriving in Kinzo’s study. However, since Nanjo and Kanon apparently arrived in the study at the same time, I have a feeling that that blue is not going to fly, and it should be assumed that Kanon and Nanjo were together for that period of time.
So, let’s go for something completely different. Kanon shot Rudolf to death from Kinzo’s study during Kinzo’s episode. He had previously stored a gun inside Kinzo’s study, and Rudolf was on the outside, with a clear line of sight from the study window to Rudolf. Either Kanon had somehow persuaded Rudolf to go there, or he had drugged him, perhaps with Kyrie’s extra strong sleeping pills, and simply placed him there himself. It was a gamble, but he managed to pick a moment when everyone’s eyes would be on Kinzo, and their backs would be turned towards the window, giving him an opportunity to shoot unnoticed. If he knew exactly where Rudolf was, he didn’t have to take long to aim. The gun’s caliber was very small, and thus Kinzo’s commotion managed hide it from the other people in the room. A bit farfetched, I agree, but I really want Kanon to be the culprit, so…
As for how he got a gun and how the closed room was created, it seems like other people have already come up with methods for that. The gun could’ve been stolen as Genji was cleaning the gun room, and it could’ve been returned the next morning as long as Kanon could access the gun room key either by taking it from Genji or through other means. It hasn’t been confirmed the key was in Genji’s possession all the time during day 2. Kanon could’ve created the closed room early in the morning of day 2 and hid in the room, avoiding detection by Kyrie by changing his hiding spot. It might be that Rudolf’s corpse was on the outside of the building the whole night, and the blood inside Rudolf and Kyrie’s room was actually from Kanon’s own hand wound, purposefully spread there in advance when he came to Rudolf’s room before 11:00 to move him outside, creating the illusion that Rudolf’s blood ended up there between 11:00 and midnight.