The following describes the truth of what happened behind-the-scenes in Turn of the Golden Witch.
Culprit: Sayo Yasuda, who committed suicide halfway through.
Before the murders: Sayo played the part of Beatrice and gave Maria the letter. She bribed Rosa with a promise of gold, to which Rosa agreed. As Sayo was fully dressed as human Beatrice, with a blond wig, Kyrie failed to completely recognize her and simply told everyone that the "woman from the portrait" had appeared.
The first twilight: Sayo invited all the adults to the chapel to look at the three gold bars she had laid out. After she had them grudgingly accept that she was the true head of the family, she gunned them down, except Rosa. The chapel door was left unlocked. Rosa pretended that it was locked in the morning to give off an illusion of a closed room.
"Illusions to illusions. The gold truth locks the lock of illusions." - Willard H. Wright
The second twilight: Sayo, dressed as Kanon, lured Jessica to her room and killed her with a gun before planting a stake in the bullet hole. She escaped.
"Illusions to illusions. Illusions that have fulfilled their role do not leave a corpse." - Willard H. Wright
The seventh and eighth twilights: Genji murdered Nanjo and Kumasawa under Sayo's orders and hid their bodies such that they would only be found after the fourth, fifth and sixth twilights were complete, giving off the illusion that the "culprit" is still around even after the sixth twilight, although Sayo had killed herself in the fourth twilight.
"Earth to earth. Illusions to illusions. No illusion can create a corpse." - Willard H. Wright
The fourth, fifth and sixth twilights: Sayo, George and Gohda went to Natsuhi's room to get the spirit mirror. The details henceforth have not been completely confirmed, but Sayo revealed herself to George, who then shook his head frantically and refused to accept it. Sayo then picked up her gun and killed both George and Gohda, crying. She then tied the gun to a cabinet and shot herself in the head, while leaving a stake next to her body. The resultant recoil causes the gun to be hidden behind the cabinet, forming a perfect closed room.
"Earth to earth. No one will deny that a coffin is a closed room." - Willard H. Wright
The tenth twilight: Genji invited Battler to the study room. What happened there is unknown. Meanwhile, Rosa tried to look for Sayo, thinking she was only playing dead, then horrifically realized that Sayo was dead and there was no one else who could turn off the bomb. Rosa tried in vain to save Maria by telling her to swim away. The bomb then went off, killing the remaining survivors.