The Man From 19 Years Ago (19年前の男 19-nen Mae no Otoko ) is a character only appearing in End of the Golden Witch and mentioned once in Requiem of the Golden Witch. During the fifth game, it seemed that Krauss and Jessica were his targets, but in actual fact, his goal is to actually frame Natsuhi for the murders he would commit as part of revenge for the injuries he recieved as a child.
In the manga adaptation of Twilight of the Golden Witch, Erika made a theory that the one who passed the calls was actually Battler reading a script written by Sayo, being bought off by the culprit and following a scenario arranged with the other adults, but unaware that said culprit really intended to kill people. However in order to retain Ange's key from Erika, Battler destroys one of Erika's blues revealing Sayo as the caller of the morning of October 5th. Despite Battler confirming caller only for this morning, Beatrice, during game of hide-and-seek, implied that she was the one calling later on as well. Interestingly enough, Natsuhi, during the first call, mentions the callers voice to be androgynous, which is completely different from the voice acting done with Battler's voice.
It is to be known that the "Man from 19 Years Ago" is more of a what-if scenario of Sayo Yasuda, and this is why her motive differs from Beatrice's motive in Episodes 1-4. While her ulterior goal of creating a murder mystery game and destroying the island remained, her main motive for creating this game before the bomb went off was not as a cry out to Battler to solve it, but simply to get revenge on Natsuhi who destroyed her life. As stated by Erika, if Sayo's motive had been what it was in the previous episodes, she would never have made Battler an accomplice (which he was in Episode 5), and would not have stopped the game right after the First Twilight.