Police have yet to formally establish a motive for the attack. However, Uematsu was put in hospital earlier this year for almost two weeks after he said he would kill disabled people.
Authorities said Uematsu had been “involuntarily committed” to hospital on 19 February, after police in the town of Tsukui contacted him in response to a letter he had attempted to pass to the speaker of the lower house of Japan’s parliament.
In the letter, Uematsu argued that the government should permit euthanasia for disabled people, said he would be willing to carry out such killings himself, and detailed how he would do it.
“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,” the letter said.
Uematsu’s letter said he could “wipe out a total of 470 disabled individuals” by targeting two facilities for disabled people during the night shift, “when staffing is low”.
“The act will be carried out speedily, and definitely without harming the staff. After wiping out the 260 people in two facilities, I will turn myself in.”
He was released from hospital on 2 March.