In February, Uematsu took a letter to the speaker of the House of Representatives in which he threatened to carry out the attack.
"I will carry out a massacre without harming the staff," Uematsu wrote in the letter, according to Kyodo News, which published a photo of the letter. "I will kill 470 disabled people. My goal is to euthanize, with their guardians' consent, seriously disabled people if they can't live at home or be active in society," he wrote, referring to the center by name. "I will carry it out at night time, when there are fewer staff on duty," he wrote.
NHK, the public broadcaster, added that Uematsu had also told his colleagues in February that seriously disabled people had no use for life and should be euthanized, leading them to call the police.
Five days after he delivered the letter, Uematsu finished working at the care facility. He was investigated by police for making the threats and sent to a hospital for an emergency evaluation for delusional behavior, local media reported, citing police officials.
He was apparently allowed to go home to his house at the bottom of a dead-end road here, overlooking lush green fields.