Six bodies, including a young girl's, were discovered Monday at a home in the southwestern Japan prefecture of Miyazaki, local police said.
The police arrived at the home owned by Yasuo Iihoshi, 72, in the city of Takachiho to find a female body outside, as well as three male and two female bodies inside the house.
Of the six bodies, three were confirmed as those of Iihoshi's wife Mihoko, 66, his 7-year-old granddaughter Yui and an acquaintance, 44-year-old Fumiaki Matsuoka.
Authorities went to the house after a family member told them his calls had gone unanswered.
A dead man found later in the day under a city bridge around 3 kilometers from the house may be his son, the police said.
The Miyazaki prefectural police said they have launched a murder investigation.