Three family members were found dead at a household in Tokorozawa, Saitama Prefecture, early Saturday morning after the father apparently went on a rampage that ended in his suicide.
Kazuo Otomo, 49, apparently died of a self-inflicted stab wound, while his wife and mother-in-law died from blows to their heads at their home around 4 a.m. Saturday.
Tokorozawa police rushed to the scene after being contacted by the fire department, which fielded a call from Daisuke Otomo, 22, who said his father had cut open his own stomach.
Authorities subsequently found Kazuo's wife Yasuko, 49, and her 73-year-old mother Fumi dead from head injuries.
The family's 23-year-old daughter was in a stable condition after being hospitalized with a fractured arm and bruises to the head. Daisuke was unharmed.
The wife was found in a first floor bedroom and her mother in a second story bedroom. Both were apparently bludgeoned to death while sleeping.
There was no evidence of burglary in the family of five's three-story home, authorities said.
The father's corpse was found on the third floor with a knife protruding from the left side of the chest. A bloody hammer was found in a sink on the third floor. No explanatory note was found.
The fire department said the family's previous home and a storehouse were completely destroyed by fire in February 2000. Local residents said the family moved into the newly built house in November, and that Otomo had not been taking his car to work recently and had been heard complaining about debts owed by his mother-in-law.