Police arrested a man on suspicion of murder Saturday after three people — including two of the suspect's relatives — were found dead at a home in Kagoshima Prefecture.
The suspect's grandmother, who is in her 80s, and his father, who is in his 60s, were living in the house in the city of Hioki, were missing, police said.
The missing man's 38-year-old son, Tomohiro Iwakura, was arrested on suspicion of strangling one of the three victims.
The suspect admitted to the charge, police said, though a motive was not immediately known.
The three victims include the woman's 69-year-old daughter-in-law, Takako Iwakura, and the latter's sister, Kuniko Sakaguchi, 72. The third victim was a neighbor, Hiroyuki Goto, 47.
The suspect was arrested for allegedly killing Goto and has suggested to investigators that he had also killed the other two, authorities said.
The missing woman's oldest son asked his wife, Takako Iwakura, to go to the house and check on his brother and mother Friday after learning that his brother had not shown up to work for several days.
He called police after he was unable to contact Takako and also asked Goto to visit the home to get a handle on the situation.
It was not immediately clear why Iwakura's sister was at the house.