The real culprit was Tsukano. His original plan was to stole the land deed that his sister had left for him but the victim had taken from him. The victim caught him while looking through the painting and threatened him to press charges so he ended up killing the victim. After killing him, Iwamatsu came so he decided to hide behind the door. Iwamatsu accidentally knocked the vase on the floor which he had taken advantage for hiding the knife. The housekeeper after hearing the noise rushed to the crime scene. Tsukano decided to pretend that he just arrived and checked the victim so that he would have an excused for the blood in his hands. Then after the housekeeper left to call the police and the ambulance, he took the vase to the garbage collection site outside hoping that the it would collected and disappear. But unfortunately it didn't so he decided to take the knife and the gloves out of it and throw it in the park pool.
