A 32-year-old man was arrested Tuesday in Hirakata, Osaka Prefecture, on suspicions that he murdered his mother, grandmother and a younger sister.
Hidekazu Shimizu was taken into custody after police found him soaked in blood, wandering in front of a convenience store. A police spokesman said Shimizu told officers he had killed members of his family.
Shimizu, whose left hand was injured, initially told police he had fallen from a high place.
"He was very calm. We went to his house with him and found two dead bodies," the spokesman said, referring to the 74-year-old grandmother and 21-year-old sister.
Police said they received a silent call from Shimizu's house at around 6:30 a.m. and sent officers there. En route, the officers spotted the son.
Shimizu's 53-year-old mother was found alive and taken to a nearby hospital, but she died four hours later.
"In the house, we found at least two knives and a big wooden hammer," the spokesman said, adding that a 30-year-old sister was also slightly wounded.
Police said Shimizu's mother, Kazuko, and grandmother, Hatsuko, were found lying on the kitchen floor, while his sister, Eiko, was found lying on the floor of another room. All three were wearing pajamas.
Near Hatsuko's body was a large wooden mallet, while a knife was found on the floor in the room next to the kitchen, and another knife was found in the hallway. The blade of one of the knives had broken off.