The man suspected of killing 34 people in an arson attack in Japan lived alone, hundreds of kilometres from the torched Kyoto Animation studio, where he played video games non-stop and “terrified” his neighbour just days earlier.

Police suspect 41-year-old Shinji Aoba caused Japan’s worst mass killing in two decades on Thursday when he went to the studio in western Japan, poured fuel around the entrance and shouted “Die” as he set the building ablaze, according to public broadcaster NHK.

Police have confirmed Aoba’s identity and said he had been previously convicted of robbing a shop. He has not been arrested because he is in hospital for treatment of heavy burns all over his body, NHK said.

Aoba lived alone on the ground floor of a two-floor apartment building on the outskirts of Omiya, a commuter suburb of Tokyo and some 500km east of Kyoto. His next-door neighbour recalled Aoba as pudgy and unkempt, with blemished skin. He kept odd hours and barely spoke to anyone.

“I’ve never seen him go out during the day, not even to the convenience store. I would regularly hear him go out around midnight,” the neighbour, a 27-year-old man who declined to be identified, told Reuters.

Music from video games blared from Aoba’s apartment at all hours, the neighbour said. On July 14, days before the attack, Aoba grabbed and threatened the neighbour over an apparent misunderstanding. It started when Aoba began pounding on the wall to complain about noise.