Media reports say the victims ranged in age from 60 to 80 years old and lived in two houses set among farms in the city of Sumoto on Awaji Island.
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Keizo Okumoto, deputy chief of the Sumoto police, said the man who was arrested, Tatsuhiko Hirano, is a neighbor of the victims.
Okumoto said major crime is rare in Sumoto, a city of 44,000 people known for its oranges, onions and Awaji beef.
