The DVD was among items confiscated during a search by the Kyoto prefectural police of the suspect’s apartment in Saitama on Friday
It is the first time for any link to be confirmed between the suspect, Shinji Aoba, and Kyoto Animation.
The company, called KyoAni by anime fans, is believed to have been involved in the production on the work of the confiscated DVD.
Aoba is said to have claimed when he was captured following the attack that he set fire to the studio because the company stole his novel. However, there are no records of Aoba applying for his novel to be made into anime by Kyoto Animation, according to the company.
The items confiscated from Aoba’s home also included a smartphone and a badly damaged large speaker, according to the sources.
The police have yet to serve an arrest warrant on Aoba on murder and other charges as he is in intensive care for severe burns at a hospital in Osaka Prefecture.
Aoba fell into unconsciousness after the attack but has recently started to show subtle responses, informed sources said. Still, a senior Kyoto police official said the suspect’s life remains in danger.
The death toll from the arson attack has reached 35.