From what I heard someone deduced that the victims are related by being online game friends because of how their names (plus the announcer) are based on the name of 4 different games.
Yumekawa Saiko: Yume = dream, Saiko = saigo = last -> Final Fantasy.
Morita Atsumi: Atsumare Dōbutsu no Mori = Animal Crossing.
Kiryu Taiji: Ryu = dragon, taiji = extermination -> Dragon Slayer.
Kanzawa Koretsugu: Kan Kore = Kantai Collection.