Police arrested a 26-year-old man who went on a stabbing spree on Tuesday at a care facility for people with mental disabilities in Tokyo that left at least 19 people dead and 25 injured.
Satoshi Uematsu was charged with mass killing, after he turned himself into police shortly after the savage stabbing, Xinhua news agency reported.
Investigative sources said the assailant—currently unemployed—used to work at the Tsukui Yamayuri-en care facility where he attacked dozens of disabled residents, may have harboured deep resentment for those with disabilities or for the facility itself.
Uematsu, who was carrying a bag full of bloodied knives and blades when he arrived at the police station, lived half a kilometre away from the facility. He is undergoing mental health checks, sources said.
The killer himself was admitted to a mental hospital in February 2016 as city officials deemed him unstable but was released later in March as his health was considered to have improved.
Prior to his hospitalisation, he reportedly wrote a letter to a lower house member of the parliament outlining his wish of "world where the disabled can be euthanised".
The attacker mentioned that the Tsukui Yamayuri-en care facility would be one of his targets.
In June last year, Uematsu came to be known to local prosecutors following an altercation with a man at a station in Tokyo during which the man sustained injuries.
The actual motive for the attack was still being investigated and it is not yet clear whether he saw his actions as emancipating the disabled or simply wanted to massacre.
Hospital staff told the media that the death toll was likely to go up as many of those injured sustained life threatening injuries.
Police reached the scene within minutes but the assailant had already driven off.
The facility can house up to 160 residents and is located 50 km from Tokyo.
Prime Minister Shinzo Abe said the government will do everything in its power to determine what and how the events at the care centre unfolded with the aim to prevent such an incident happening again.
Tuesday's attack marks the worst mass killing in Japan since 2001 when 16 people died in an arson attack at a video parlour in Osaka.