The suspect in last week’s deadly arson attack on a Kyoto Animation Co. studio may have walked for hours scouting the company headquarters and the nearby area the day before the fire, even bringing gas containers to the site, investigative sources said Tuesday.

Shinji Aoba, 41, who allegedly ignited the blaze that left 34 people dead in the three-story studio building in Kyoto on Thursday, likely bought gasoline containers at a hardware store located 5 kilometers from the studio and transported them in a handcart to the site Wednesday, they said.

The walk could have taken more than an hour as anyone trying to get to the anime studio from the store needs to cross a river and pass through a complex residential area.

Investigators have received eyewitness accounts placing a man resembling the suspect in the area on Wednesday, according to the sources.

Surveillance cameras at the hardware store captured a man believed to be Aoba in a red shirt and blue jeans purchasing the containers the same day.

There is no information indicating he used public transportation afterward, the sources said.

Meanwhile, officials on Monday searched for an explanation as to why a blaze ripped so quickly through the famed animation company’s studio, amid reports that smoke spread so fast a majority of the victims who tried to flee through a rooftop door could not open it in time to escape.

In a gruesome reversal, Kyoto police said that of the 26 people whose autopsy results have been released, 20 burned to death, three suffered carbon monoxide poisoning and two suffocated. The cause of death of one was undetermined. Previous reports indicated most were likely killed by smoke.

Nineteen of the dead were found piled on top of each other on a stairway from the third floor to a door leading to the roof, with some early reports suggesting it could not be opened from the inside.

But police quoted by NHK on Monday said investigations had shown that while the door could be opened from the inside, smoke from the blaze appeared to have spread so fast it overcame the employees before they could do so.

Junzo Yamamoto, head of the National Public Safety Commission, offered flowers at the site before stepping into the building’s blackened hulk to inspect it.

“The question of how we can prevent this kind of incident is extremely difficult to answer,” Yamamoto told reporters. “Before getting there we need to clarify the whole picture.”

Fire officials told a municipal assembly panel that everything at the building had complied with the fire code and they were investigating why so many lives were lost, NHK said.

The company had run sufficient fire drills and taken all steps required by law, including “hanging walls” designed to stop smoke from rising, it added.

Earlier, experts said a spiral staircase near where the fire was lit acted as a chimney, carrying the smoke upward through all three stories. Survivors have described a “dark mushroom cloud” rising up the staircase.

The tragedy left the company at a loss, it said in a statement late Sunday.

“All of these people were our talented, precious colleagues,” it said. “Both for us here, as well as the animation industry as a whole, this is a huge blow.”