An elderly couple and a woman were found dead Sunday in Kobe, western Japan, and the couple's 26-year-old grandson was arrested for possessing a kitchen knife, police said.
The suspect's mother and another woman were also injured, with all five victims suffered cuts and bruises, according to the Hyogo prefectural police.
The man, Kanami Takeshima said he "just wanted to attack and stab anyone," according to the police, who have launched a murder investigation.
The suspect lived with his grandparents, Tatsuo Nambu and his wife Miyuki, both 83, and his mother, Tomoko Takeshima, 52, and was arrested on suspicion of violating the firearms and swords control law at a shrine close to the residence.
A police officer found the elderly couple collapsed at the scene after Nambu called police requesting help. The couple were later confirmed dead, while another woman, 79-year-old neighbor Yaeko Tsuji, was found dead nearby.
The suspect's mother and Misao Maekita, a 65-year-old neighbor, were not in a life-threatening condition.