About 60 nearby residents were evacuated to a local junior high school, according to local media, and the authorities warned others to stay indoors.

A witness to the attack told NHK that he was working in a field when a young woman ran toward him, pleading for help as a man wearing camouflage, a hat and a mask chased after her. The man then stabbed her in the back, causing her to fall down, and then stabbed her again in the chest.

“I asked him, “Why you are doing this?” the witness told the broadcaster. “He answered ‘I killed her because I wanted to kill.’”

The suspect left the scene but returned with a rifle after two police officers arrived in response to the stabbing, the witness said. Holding the muzzle against the window of their police car, the suspect shot twice and fled the scene again.

The brutality in the emerging details of the assault, including the stabbing of a woman in public and the killing of police officers, made it “an extremely rare” event, said Dr. Fabio Gygi, chairman of the Japan Research Centre at SOAS University of London.