The defense team for the man accused of carrying out a 2019 arson attack that killed 36 people at a famous Japanese anime studio in Kyoto called for his acquittal at the trial's first hearing Tuesday, arguing he was not mentally competent at the time.

Shinji Aoba, 45, admitted at the Kyoto District Court to the attack, deemed as one of Japan's worst-ever mass murders. He faces five charges including murder over the blaze at the Kyoto Animation Co. studio's premises, according to the indictment.

"I felt I had no other option but to do what I did," said Aoba, from Saitama Prefecture, north of Tokyo, but added that he "did not anticipate that so many people would die."

Another 32 people were also injured in the attack, and prosecutors are likely to seek the death penalty for his actions.

File photo shows smoke billowing out of the three-story studio of Kyoto Animation Co. in Kyoto on July 24, 2019, after it was set on fire in an arson attack. (Kyodo) 

The studio, often referred to as "KyoAni," is known internationally for producing a number of popular animation works, including "K-On!" and "The Melancholy of Haruhi Suzumiya."

Wearing a face mask and seated in a wheelchair, Aoba, with close-cropped hair, said, "I now think that what I did was excessive."

The defense team said Aoba was suffering from delusions and believed he was fighting back against a "dark figure," arguing that even if he is convicted, he should be given a reduced sentence because of what they said was his state of diminished capacity.

His lawyers also said the studio's structure may have led to the large number of fatalities.

The prosecutors said Aoba wrongly believed that Kyoto Animation had plagiarized a novel he had entered into a contest run by the firm and that he was under surveillance by the authorities. But they said he was not controlled by such delusions and can be held fully responsible for the attack on the studio on July 18, 2019.

In their opening statement, the prosecutors also revealed that on June 18, a month before the attack, Aoba had planned an indiscriminate attack at Omiya Station in the city of Saitama. The prosecutors said that he brought six blades with him to the station, but ultimately abandoned the idea.

About 500 people, including Kyoto Animation fans, lined up near the court from 7 a.m. Tuesday, vying to get just 35 courtroom seats made available to the general public.

After the first hearing of the lay judge trial, 23 more sessions are expected to follow before the ruling is handed down on Jan. 25, 2024.

When the police detained him near the studio shortly after the attack, Aoba admitted to setting the studio on fire, saying the company had "stolen a novel" from him.

Photo taken on Sept. 5, 2023, shows a courtroom at Kyoto District Court that held the first hearing of a trial over the 2019 arson attack on anime studio Kyoto Animation Co. that killed 36 people. (Pool photo)(Kyodo)

Before the attack, Kyoto Animation held public contests for draft novels with the promise that the winners would get their stories turned into animated shows. However, the company says none of its shows were based on Aoba's submitted works.

Following his arrest, Aoba told investigators he had thought he could kill many people by using gasoline but also said he had thought there were only about two victims.

Aoba himself sustained life-threatening burns and underwent intense treatment before he was arrested in May 2020. He made his first court appearance in June that year for a pre-trial detention hearing, lying on a stretcher.

The prosecutors indicted him in December 2020, claiming after conducting a psychiatric evaluation that he can be held criminally responsible for his actions, despite his documented history of mental illness.

Tomoyuki Mizuno, a professor in criminal law at Hosei University Law School and a former judge, said the court's conclusion was harder to predict than the debate set to unfold.

"Was the crime committed under delusions, or was it in the accused's character? It's easy to see what the arguments will focus on, but making a judgment is difficult," he said.

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