Umineko: When They Cry - Season 1 Episode 4 Blunder

Everybody tries to determine how Eva and Hideyoshi could have been killed when an odd smell begins to fill the mansion. Kanon goes to investigate the boiler room along with Kumasawa, but is mortally wounded in the process. The rest of the family and staff arrive and discover the dying Kanon, as well as Kinzo's partially incinerated body. They decide to retreat to Kinzo's study, which should be the safest room in the house. After they enter, however, a letter from Beatrice mysteriously appears. Since Genji, Nanjo, Kumasawa, or Maria are the only possible suspects for planting the letter, Natsuhi forces them to leave the study. Later that night, the phone rings with Maria singing on the other end. Natsuhi, Battler, George, and Jessica rush downstairs to find Genji, Nanjo, and Kumasawa murdered and Maria standing in the corner, still singing.