OSAKA (Kyodo) -- A man convicted of the 2019 fatal arson attack on a Kyoto Animation Co. studio dropped his appeal against his death sentence because of his dissatisfaction with his defense's claim he was delusional, and his lawyers are now seeking to have the decision nullified, a source close to him said Tuesday.

The source said Shinji Aoba, 46, later regretted withdrawing his appeal against the Kyoto District Court ruling in January 2024 over the incident that killed 36 people and injured 32 at the internationally renowned animation studio.

The Osaka High Court said Aoba submitted a withdrawal notice for his appeal on Jan. 27. The source said his defense then filed a petition on Jan. 30 contesting its validity, which the court accepted the same day.

A closed-door three-party conference was held at the high court on Feb. 28, where the defense explained Aoba's withdrawal of his appeal, the source said. The court is expected to rule on its legitimacy after reviewing arguments from both the defense and prosecution.

The district court acknowledged Aoba had a delusional disorder but determined he was neither in a state of insanity nor mental impairment. It found him fully responsible for his actions, sentencing him to death.

Afterward, Aoba and his defense challenged the death sentence, with the lawyer also submitting a written appeal to the high court, asserting the judgment on his criminal responsibility was flawed.

A bereaved family member of a victim who visited Aoba at a detention house in Osaka following the first trial verdict was quoted by the source as saying that Aoba expressed frustration that a psychiatrist had deemed him delusional.

The ruling by the district court said Aoba intruded into the Kyoto Animation studio's premises at around 10:30 a.m. on July 18, 2019, in which 70 employees were working. He set the building on fire with gasoline, triggering one of Japan's worst mass murder cases.

Kyoto Animation, often referred to as "KyoAni," is known worldwide for producing hit anime works including "K-On!" and "The Melancholy of Haruhi Suzumiya."