Police in western Japan say a man arrested in connection with the killing of three family members had worked with one of the victims.
Iwata Kenichi, who was 51, and his 80-year-old father and mother were stabbed to death at their home in the city of Niihama, Ehime Prefecture, on Wednesday.
Police officers rushed to the family's home after the mother informed them they were having trouble with a visitor. The police say they found two members of the family lying inside the home and the other near the entrance.
They arrested a 53-year-old unemployed man, Kono Satoru, at the scene on suspicion of violating the law for controlling the possession of firearms or swords.
Police investigators quote the suspect as telling them he was carrying a knife with an intention to kill.
They say Kono used to be a colleague of Iwata Kenichi.
The investigators also say the suspect had visited Iwata's home a few times before. The police are looking into what might have happened between the two men.