At least 19 people died and 25 others were injured - 20 of them seriously - in a savage attack at a home for the disabled near Tokyo early yesterday morning.
Satoshi Uematsu, 26, allegedly stabbed his victims in their sleep at the facility in Sagamihara city, 50km west of central Tokyo, in the deadliest attack in post-war Japan.
The crime has no apparent links to Islamist terrorism, top government spokesman Yoshihide Suga told a news conference yesterday.
Prime Minister Shinzo Abe told a Tokyo gathering: "The lives of many innocent people were taken away and I am greatly shocked. We will make every effort to discover the facts and prevent a reoccurrence."
Uematsu, who has been charged with murder and trespass, worked at the Tsukui Yamayuri Garden facility for more than three years until he quit in February.
I have an impression the suspect aimed at (stabbing people's) necks. He may have held a strong intention to kill.
DR TAKAO ARAI, head of Hachioji Medical Centre, where four of the injured were admitted.
Killing incidents in Japan
Where: Tokyo subway system
What happened: Members of the doomsday cult Aum Shinrikyo released sarin gas in the Tokyo subway system, killing 13 people and sickening thousands of commuters in Japan's most notorious attack.
One of the suspects in the gas attack was arrested in the town of Sagamihara, where yesterday's attack took place, in 2012.
Where: JR Shimonoseki station, Yamaguchi prefecture
What happened: A 35-year-old man, Yasuaki Uwabe, drove a car into the main train station in the south-western city of Shimonoseki, then randomly stabbed passers-by, killing five people and wounding 10.
Where: A school in Osaka
What happened: A mentally disturbed man, Mamoru Takuma, 37, armed with a kitchen knife went on a stabbing spree at Ikeda Elementary School in the posh suburbs of Osaka, killing eight youngsters. He was a janitor at another school.
Where: Tokyo's Akihabara district
What happened: On the anniversary of the Osaka school attack, disgruntled auto worker Tomohiro Kato, 25, ploughed a truck into a crowd of shoppers at a busy intersection before jumping out and stabbing people, leaving seven dead and 10 wounded.
After that rampage, Japan banned possession of double-edged knives with blades longer than 5.5 cm.
Where: A video shop in Osaka
What happened: An arsonist, Kazuhiro Ogawa, 46, killed 16 people in a fire at an all-night video shop that offered adult films in small rooms. The divorcee had lost his job and was living alone after his mother died.
Where: Awaji Island, Hyogo prefecture
What happened: Five people were stabbed to death at a home in rural Japan by "social misfit" Tatsuhiko Hirano, 40, who lived just 100m away in the same city of Sumoto.
Where: A shopping mall in Hokkaido
What happened: A 33-year-old man, Nobuyuki Matsuhashi, who had been treated for mental illness, stabbed a woman to death and wounded three others in a random attack at the Aeon Mall Kushiro-Showa complex in the city of Kushiro.
AGENCE FRANCE-PRESSE, JAPAN TIMES, KYODO NEWS AGENCY
He turned himself in to the police shortly after 3am local time (2am Singapore time), confessing to the rampage and saying he "wanted to rid the world of disabled people".
This was not the first time he had made such comments. On Feb 14, he wrote to the local lawmaker saying: "I envision a world where a person with multiple disabilities can be euthanised, with an agreement from the guardians, when it is difficult for the person to carry out household and social activities."
Five days later, he told a colleague there was "no reason for the severely disabled to continue living", and distributed fliers bearing such messages to nearby residents. He quit his job when the police were called in, and was promptly hospitalised for a mental disorder and paranoia.
But he was discharged 12 days later after his doctor deemed that he was no longer a threat to society.
In the February letter, Uematsu described methods of assault similar to those he used in the attack. He broke into the compound with eight dormitory-like rooms by smashing a first-floor window.
The facility had eight employees and one security guard working overnight. Closed-circuit TV camera footage showed Uematsu stopping a Honda near the facility at 1.37am, then running to his car and speeding away at 2.50am - 20 minutes after a worker called the police.
Uematsu, a former elementary school trainee teacher, posted on his Twitter account at about 2.50am: "May the world become peaceful. Beautiful Japan!!!"
Police later recovered three bloodied knives from his car.
The home had 157 long-term residents as of last month. All have intellectual disabilities, and some have physical disabilities, news reports said. The victims were nine men and 10 women, aged 19 to 70.
Four of the injured were admitted to Hachioji Medical Centre, where its head, Dr Takao Arai, told reporters: "I have an impression the suspect aimed at (stabbing people's) necks. He may have held a strong intention to kill." Sagamihara resident Susumu Fujimura said: "It makes you weep to think of somebody just murdering (the defenceless)."
Uematsu's father, a community leader, told Asahi Shimbun in the afternoon: "It just happened this morning... Sorry but please give me more time to gather my thoughts."