One day before he tried to hand a letter to a top Japanese lawmaker offering to kill hundreds of disabled people, the suspect in Japan's worst mass killing in decades tweeted: "I don't know if it's right, but action is the only way."
Less than six months later, Satoshi Uematsu, 26, was arrested on suspicion of stabbing 19 people to death and wounding dozens of others as they slept at a centre for the disabled where he had worked for more than three years until February.
Police have yet to comment on the motive for Tuesday's killing spree, which has shocked a nation with one of the lowest crime rates in the world and where mass murders are rare.
Information about Uematsu is still emerging, but interviews with neighbours and posts on his Twitter account paint a picture of an outwardly polite young man who became obsessed with the people being cared in Sagamihara town, about 40km southwest of Tokyo.
A Twitter account carrying Uematsu's name and which domestic media said was used by the suspect indicated he was a fun-loving young man who enjoyed karaoke and beach parties and wanted to quit smoking.
Uematsu had come to authorities' attention in February, when he said he could "obliterate" 470 disabled people.
"I am fully aware this is a statement that defies common sense," he said in letters addressed to the speaker of parliament's lower house, a copy of which was obtained by Kyodo news agency.
"However, I could not stand idle as I thought about the exhausted look on the faces of their caretakers, the crazed look in the eyes of the staff working at the facilities, and, in the best interest of Japan and the world, I have been moved to take this action today."
He added: "My goal is a world in which the severely disabled can be euthanised, with their guardians' consent, if they are unable to live at home and be active in society."
Uematsu promised in the letters to execute the killings swiftly, without hurting staff and said he hoped to be found "not guilty by reason of insanity".