A deadly incident in central Japan on Thursday claimed the lives of two women and two police officers. The attacker's possible motives are being revealed that he thought the women looked down upon him.

Police arrested a male suspect Aoki Masanori, who runs a local farming business in Nagano Prefecture.

Two older female residents living nearby were stabbed to death while they were apparently taking a walk together. A witness said when police officers arrived at the scene, Aoki approached their patrol car and shot them at close range with his hunting rifle.

After the attacks, Aoki holed himself up in his home for about 12 hours and his father tried to persuade him to come out and surrender.

Police say Aoki then told his father that he thought the two women, who he apparently did not know well, were making fun of him as a "loner" when they were taking a walk and chatting.

The father reportedly said his son often overreacted to the word "loner" as he was bullied and teased when he was a university student.

Aoki dropped out of university and his father reportedly helped him take part in a group working to preserve a local festival. But after a few years, the son stopped taking part in the group.

A man who worked with Aoki, explained that the son was not a very active member of the group. He said Aoki did not speak with others unless someone talked to him.

A social psychology expert says people who have few interpersonal experiences tend to feel lonelier if they cannot get along well with others.

Igarashi Tasuku, associate professor of Nagoya University, said, "Repeatedly going though such failures could lead to what is called cognitive bias, where an individual begins to distrust others and finally would not trust anyone."

Igarashi added it is generally believed among psychology experts that loneliness alone would not lead to such vicious attacks, and therefore some different cause was apparently responsible.