Yeah, that's right. You win, Rika.
At 1 AM, Kinjo decides to have a drink with a friend (the culprit) who is standing outside his window. Genji brings the vodka over, just as Kinjo wanted.
However, after Genji leaves, Kinjo asks the culprit if they want some vodka too, and they do. Kinjo calls Genji for more vodka, and Genji brings it to him. Kinjo then sets the chain on his door and jumps out of the window toward the culprit. Then, after Kinjo hands the culprit the vodka outside, the culprit smashes the bottle against Kinjo's head, killing him instantly. Culprit drags Kinjo to their own room, which is next door, and shoots his head off. This obscures the true cause of death, the bottle.
The next morning Genji knocks at Kinjo's door, waking the culprit up. He tries to enter, but the chain is set, so he goes to get the cutters. The culprit draws a big red circle on their own door. They then go back inside the room and hide in the closet.
Genji returns to see the red circle, assumes it is Kinjo's room, and cuts the chains on it. Inside he finds Kinjo's corpse. Genji checks the bedroom, and then the windows, which are locked. He then checks the bathroom, and then the closet. During the time Genji checks the bathroom, the culprit hides under the bed. After Genji checks the whole room, he leaves. The culprit also leaves, taking the chain cutters Genji had left behind.
Finally, the culprit draws a red circle on Kinjo's door and leaves. Genji returns to this door, believing Kinjo's corpse should be inside, when it never was!