The 41-year-old man apprehended for the Thursday attack, Japan's worst mass killing in 18 years, at three-storey studio of Kyoto Animation Co. in western Japan was identified by the police as Shinji Aoba.
He told the police that he started the fire because the company stole his idea for a novel, Kyodo News reported, citing investigative sources on Friday. Over 30 people were injured in the incident.
The man screamed "Die!" as he entered the building and is believed to have doused it with what appeared to be petrol and set it ablaze. About 70 people were believed to have been working inside the building at the time.
More than 30 fire engines had to be deployed to the scene to deal with the inferno. A number of knives and knife-like objects were also found at the scene, although investigators were yet to determine if they belong to the man.
The man apprehended for the arson attack is believed to be a resident of Saitama Prefecture near Tokyo and is currently being treated in hospital for injuries he sustained in the fire.
He is being treated for burns on his face, chest and other parts of his body, and the police plan to question him thoroughly after he recovers.
( With inputs from IANS )