Police arrested a 31-year-old man in Nakano, Nagano Prefecture, on Friday after the murder of two police officers — a very rare case in Japan — as well as two others.

Masanori Aoki was arrested over the murder of one of the police officers, with further arrests likely to follow for the other slayings. A woman was also stabbed to death, and another woman, injured near the Aoki family home, was confirmed to have later died.

Aoki is the eldest son of Masamichi Aoki, who was the speaker of the Nakano Municipal Assembly. Shinano Mainichi Shimbun reported Friday that Aoki's father had resigned as an assembly member.