The police have identified the suspect as Masanori Aoki, the 31-year-old son of the Nakano city assembly speaker, Xinhua news agency reported.
The suspect was taken into custody on suspicion of murder after barricading himself in his father’s home near the city of Nakano, northwest of the capital Tokyo, at about 4.30am (19:30 GMT) on Friday.
On Friday, Japanese police apprehended a man who had holed up in a building after reportedly killing four people in a gun and knife attack, including two police officers.
The guy was apprehended outside a farm in Nakano, Nagano area, with police confirming a fourth casualty overnight: an elderly woman who was found wounded at the site and subsequently declared dead.
Another lady and two police officers were already reported deceased in the incident.
Police told AFP that the 31-year-old suspect was apprehended at about 4:30 a.m. (1930 GMT Thursday) and was subsequently formally arrested on suspicion of murder with a suspected hunting rifle.
The rampage in a rural area of the western region was a rare instance of violent crime in Japan, which has a low murder rate and some of the world’s toughest gun laws.
No motive has yet emerged in the killings, nor has the suspect been formally identified, though several local media reported he is the son of the speaker of Nakano’s city assembly.
“We pray for the souls of the deceased and express our heartfelt condolences to the bereaved families,” top government spokesman Hirokazu Matsuno told reporters.
“Police are investigating to uncover the whole picture of the incident, including how the crime developed and its background.”
‘Because I wanted to’
The attack started on Thursday afternoon, when a local man working on a farm saw a woman “running from the road saying, ‘help me’,” he told national broadcaster NHK.
“Behind her came a man wearing camouflage and carrying a large knife, who stabbed her in the back,” the 72-year-old witness said.
He said he called emergency services while neighbours tried to resuscitate the woman.
The attacker announced: “I killed her because I wanted to,” according to an eyewitness cited by Kyodo news.
Local media said he then fired what has been described as a hunting gun at police officers who arrived at the scene.
The officers were inside a patrol car and the attacker placed the weapon against a window of the vehicle and fired twice, NHK reported.
The slain officers were identified as Yoshiki Tamai, 46, and Takuo Ikeuchi, 61.
Local media said the man then barricaded himself inside his father’s home, where he remained most of the night, with occasional gunshots heard.
Two women, including the suspect’s mother, escaped the house, one at around 8:35 pm and the other soon after midnight.
The suspect was finally detained. A woman was found at the scene with injuries and later pronounced dead.
Japan was left reeling in July last year when former prime minister Shinzo Abe was shot dead in broad daylight with an apparently homemade gun.
Abe’s accused assassin, Tetsuya Yamagami, reportedly targeted the politician over his links to the Unification Church.
And last month, a man was arrested for allegedly hurling a pipe bomb-like explosive towards Prime Minister Fumio Kishida as he campaigned in the western city of Wakayama.
Kishida was unharmed and a man arrested on the scene will undergo a three-month psychiatric examination, a regional court said this week.
The suspect has reportedly remained tight-lipped about his motive for that failed attack.
The attack began on Thursday afternoon when a local man working on a farm saw a woman “running from the road shouting, ‘help me’,” he told national broadcaster NHK.
“Behind her was a man wearing camouflage and carrying a large knife, who stabbed her in the back,” the 72-year-old witness added.
The suspect is accused of shooting dead two police officers who arrived at the scene after the witness called emergency services.
The two officers, who were allegedly shot in their car, and the woman were taken to hospital where they were pronounced dead within hours.
Another elderly woman also died after an apparent attack. She had been lying on the ground outside the house since Thursday afternoon and police had been unable to get to her, media said.
The rampage in a rural area of the western region was a rare instance of violent crime in Japan, which has a low murder rate and some of the world’s toughest gun laws.
A view of the two-storey house where the suspect hid from the police. A TV news crew are filming the building. There is a field in front.
No motive has yet emerged in the killings, nor has the suspect been formally identified, although several local media reported that he is the son of the speaker of Nakano’s city assembly.
“We pray for the souls of the deceased and express our heartfelt condolences to the bereaved families,” top government spokesman Hirokazu Matsuno told reporters.
“Police are investigating to uncover the whole picture of the incident, including how the crime developed and its background.”
Few other details were known about the attack, including the suspect’s motive.
Nagano prefectural police are due to hold a press conference later on Friday.
Japan was left reeling in July last year when former Prime Minister Shinzo Abe was shot while he was campaigning,
Last month, a man was arrested for allegedly throwing a “smoke bomb” towards Prime Minister Fumio Kishida as he campaigned in the western city of Wakayama.
Kishida was unharmed and a man arrested at the scene will undergo a three-month psychiatric examination, a regional court said this week.
