Hanako of the Opera

Hanako of the Opera (オペラ座の花子くん) is a special event hosted by AidaIro on their Twitter based on The Phantom of the Opera. It began on April 18, 2020, at 8:00 PM JST and features several puzzles.

Introduction
Say, have to heard the rumors? About the incident that occurred in the opera house of the Flower Capital. Someone stole the voice of the troupe's top singer, or so they say.

The suspects are the opera troupe's members, the conductor, and the manager. Perhaps, this is the work of the phantom who's infiltrated the opera house...

Do you know who is culprit?