A teenager was arrested Saturday in Ako, Hyogo Prefecture, on suspicion of killing his grandparents, local police said.

The teen, 19, was arrested after calling police Friday afternoon to report finding his 69-year-old grandfather and 64-year-old grandmother collapsed and bleeding at their home.

The couple's bodies bore multiple cuts and stab wounds, the police said. They are believed to have been killed between Wednesday afternoon and the time the police were called, they said.

The teen has admitted assaulting the pair, though the murder weapon has not yet been found, they said.

The suspect, who was not identified as he is a minor, was adopted several years ago, the police said.