The suspected arsonist behind the deadly fire at an animation studio in Japan was identified Friday as Shinji Aoba, who served time in prison for robbery and has been treated for mental health issues, according to reports.

Shinji Aoba, 41, carried out the attack at the Kyoto Animation building in Tokyo, killing 33 people, because he believed his novel had been plagiarized, according to police and local media.

He is accused of wheeling a cart carrying at least one bucket of gasoline to the building’s entrance, shouting “You die!” and setting off the worst mass killing in Japan in two decades, Nippon TV reported, citing police.

“I did it,” Aoba, who is hospitalized with severe burns, told authorities, Kyodo news reported.

Aoba, a resident of the Tokyo suburb of Saitama, is believed to have bought two 20-liter (5-gallon) gas cans at a hardware store and prepared the incendiary attack in a park near the studio after traveling by train, according to Reuters, which cited Nippon TV.

A Kyoto Fushimi Police spokesman said authorities were not yet aware of a link between the suspect and the studio, according to CNN.

Twelve men, 20 women and another person whose gender was unknown died in the conflagration, which also left 35 others injured. All of those who perished were studio employees, CNN reported.

Investigators told NHK that Aoba was indicted in 2012 for a convenience store robbery and sentenced to 3½ years behind bars.

After completing his sentence, he briefly lived in a shelter for former convicts before moving to his current apartment, where he lives on welfare, the news outlet reported.

He also had run-ins with his neighbors over noise that police have responded to.

Thursday’s fire spread so rapidly that many of the 74 people who were in the building did not have time to flee, police told CNN. Several people suffered broken bones when they jumped from the second and third floors.

On Friday, anime fans and mourners arrived at the ravaged building, where they laid flowers in tribute to the victims.

“I was so encouraged by the KyoAni works,” said one young fan, calling the studio by its popular name, according to CNN. “I have no words to say in sorrow.”

Kyoto Animation CEO Hideaki Yata said the company had received death threats by mail, which had been sent to authorities.

“They are the people who carry the Japan’s animation industry on their shoulders. I can’t bear to accept the fact they are being hurt or losing their lives,” he said.

The studio received a death threat through its website in October 2018, police said.

The company filed a formal complaint to police but they were unable to identify the sender.