2023 Nagano attack

On the evening of 25 May 2023, a masked man wearing camouflage attacked a woman in Nakano, Nagano Prefecture, Japan, chasing her while carrying a large knife and stabbing her in the back, according to a witness account. When police officers arrived at the scene, the suspect fired what appeared to be a hunting rifle, striking multiple people. Following the shooting, the suspect took refuge inside the residence of Masamichi Aoki, the speaker of the Nakano City Assembly. During the ensuing siege, two of the suspect's relatives, including his mother, managed to escape the home. He was apprehended in the early hours of the following day, at 4:37 a.m., and was identified as Masamichi Aoki's son.

Four people were killed in the attack: a woman in her 40s, and two police officers, Inspector Yoshiki Tamai (46) and Sergeant Takuo Ikeuchi (61). The two officers were killed at close range with shotgun slugs and were reported not to have been wearing bulletproof vests while responding to the emergency call. A separate injured woman who could not be transported from the scene was pronounced dead at 4:54. The Nagano Prefectural Police requested an arrest warrant for the suspect on suspicion of murder on the morning of 26 May. The National Police Agency deployed the Tokyo Metropolitan Police Department's Special Investigation Team and the Kanagawa Prefectural Police's Special Assault Team to assist local police.

The suspect was identified as 31-year-old Masanori Aoki, born in mid-1991, a farmer from the Nakano suburb of Edu who held a valid firearm permit. His motive has not been established. When a witness asked why he had stabbed the woman, he reportedly said, "I killed her because I wanted to." During police interrogation, he later stated that he believed the women he killed had been talking badly about him. His father, Masamichi Aoki, resigned as speaker of the Nakano City Assembly on the day of his son's arrest.

At trial, defense lawyers argued that Masanori Aoki had diminished capacity due to schizophrenia and sought a life sentence rather than execution. On 14 October 2025, he was sentenced to death for the murders.

In the immediate aftermath, area residents were compelled to find alternative overnight accommodations, and a local school was closed. Once the arrest was confirmed, authorities informed the community that residents could resume normal activities.