The 26-year-old Japanese man who killed 19 mentally disabled people in a stabbing rampage had written a letter to Japan’s parliament detailing his plan months before he carried out the attack. Satoshi Uematsu was fired from a facility for the disabled just outside of Tokyo. On Tuesday, he killed or injured about a third of the 150 patients in less than an hour, mostly by slashing throats. Twenty-five people were wounded, and 20 of those people are in critical condition. In February, Uematsu wrote a letter to the parliament asking that all disabled people be killed in “a world that allows for mercy killing.” He reportedly wrote that he could kill 470 disabled people in “a revolution” and foretold of an attack he wanted to carry out on two facilities. The letter was forwarded to local police. It’s unclear why police didn’t take the threat seriously. Kanagawa Gov. Yuji Kuroiwa has since apologized for not acting on it. The attack is the deadliest act of mass murder in Japan since the end of World War II.