Tomohiro Kato told the Tokyo District Court on Tuesday that he was "fully responsible" for the 2008 vehicle and stabbing massacre in Tokyo's Akihabara district and said he had been harassed on a mobile phone bulletin board in the leadup to the attack.

Kato, 27, a former temporary worker, made the remarks in response to questions posed by his lawyers. He is on trial for the random killing of seven people and wounding of 10 others on June 8, 2008, when he drove into a crowd with a rented truck and then started stabbing people before being subdued.

Asked why he went on the rampage, Kato said: "There are three reasons. One is my own thinking. The two others are harassment against me on the bulletin board, and my way of life, which was deeply dependent on the board.