Japanese police have named a 41-year-old man suspected of carrying out an arson attack on an animation studio that killed 34 people.

Witnesses said Shinji Aoba confessed to the massacre as he was arrested. He was allegedly overheard telling police he started the fire because the studio, Kyoto Animation, had copied his ideas and stolen his novel.

Were it not for the three-storey burnt-out building visible over the tops of the houses along the narrow backstreets of Rokujizo in the Fushimi Ward of Kyoto, it would be hard to believe the area was the scene of the biggest mass killing in Japan in living memory.

On Thursday, Aoba allegedly burst into the building carrying 40 litres of petrol and a bag full of hammers and knives and set fire it. In addition to the 34 studio staff who were killed in the blaze, 35 were injured.

Play Video 1:29 KyoAni fire: arson attack at Kyoto Animation studio – video report

A chalk outline on the ground where Aoba was found lying is just behind a police cordon blocking the streets leading to the studio, where young artists created anime that won fans across Japan and beyond. The narrow streets had made it difficult for the dozens of emergency vehicles to reach the building, according to witnesses.

Keiyu Hada, a high-school student, was walking past the studio on Thursday morning with his mother when he saw the studio ablaze.

“We were about 10 metres away, but the heat was so intense on my face it was unbearable. There were three people outside that I saw had come out of the building. They were on fire; their clothes and hair were burning,” said Keiyu, whose family looks after and lives at the local Buddhist temple.

“After a while, I couldn’t stand to look, so we went back to the temple. Some people from the neighbourhood came with us, they thought there might be another explosion.”

Facebook Twitter Pinterest Mourners leave floral tributes at the scene of the blaze. Photograph: Jiji Press/EPA

There were firefighters at the scene but it took a further 10-15 minutes before more arrived with hoses, Keiyu said. “I wonder if they had been quicker more people could have been saved, but I think it was hard for them to drive down there.”

Under grey skies on Friday, a steady stream of mourners stopped to lay flowers. Others simply put their hands together and made long, silent bows in the direction of the building’s charred remains.

Shoumyou Oh, a 23-year-old from China, made the trip down on the bullet train from Tokyo, where he is studying Japanese, to pay his respects.

“Kyoto Animation’s productions are very popular in China – I have known them since I was in junior high school. They make anime and stories that touch your heart. This news was trending top yesterday on Weibo, the Chinese Twitter,” he said.

“I can’t understand why someone would do this. I want to hear the reason from the criminal.”

Shortly after, the police had named the man they have in custody in hospital as Aoba.

“He is badly burned on his hands, feet, chest and face; his hair has been burnt off. We are waiting for word from the doctors as to when we can question him,” Hiroyuki Sakai, the deputy chief of the local Fushimi police station told the Guardian.

Sakai confirmed 19 bodies had been found on the third floor and the staircase leading to the roof, with some piled on top of others, suggesting they were scrambling to escape.

Facebook Twitter Pinterest Investigators inspect the scene. Photograph: Buddhika Weerasinghe/AFP/Getty

Fushimi Ward usually had a low crime rate, said Sakai, and there had not been a single murder there last year, though a woman fatally stabbed a man in March during a domestic dispute.

About 100 police and medical examiners are working on the KyoAni case. An investigation headquarters has been set up in a gym in the the Kyoto police training centre as the local station is too small to cope.

“Five autopsies were carried out today. The bodies of the victims are in different states, depending how and where they died,” Sakai said.

“There will be more autopsies done in the coming days. Once everyone has been identified and the families informed, we will release the names of the victims.”

The suspect has yet to be arrested or charged. If he is, prosecutors will almost certainly seek the death penalty.