Three bodies with head wounds were discovered at a residence in Nagano Prefecture, on Tuesday night in what police suspect is a murder case.
Police rushed to the house of Takenori Ichikawa after emergency services received a call around 11:15 p.m. on Tuesday in which he said someone was hurt.
Police discovered three bodies, two of whom were Ichikawa's children. The three were taken to hospital where they were pronounced dead, according to police and investigative sources.
The two children were identified as Anna, 22, and Naoto, a 16-year-old high school student.
The identity of the other person has not been released, but he is a 35-year-old man unrelated to the family.
Ichikawa and his wife were unharmed, according to the police.
The incident occurred in a residential area located around 1 kilometer southwest of Tekuno-Sakaki Station.