The suspect in the deadly arson attack on a Kyoto Animation Co. studio, who suffered life-threatening burns across 90 percent of his body, has become the first person with such extensive critical burns to undergo surgery without using donor skin, medical sources said Tuesday.

Following the July fire, which killed 36 people and injured 33, Shinji Aoba was left in critical condition with burns that had destroyed the innermost skin layer, the subcutaneous tissue, the sources said.

Donor skin is typically used in initial treatment for such widespread burns because only a limited part of the patient’s own skin is left available for transplanting.

But the 41-year-old has undergone surgeries using prosthetic skin and his own skin only, even though he had third-degree burns, which destroy the entire thickness of the skin from the surface to underlying tissue.

The details of the procedures are expected to be presented in an academic conference next year.

The hospital in Osaka Prefecture prioritized the use of donor skin for the victims of the attack due to the risk of a shortage amid a chronic lack of donors.

The survival rate drops dramatically when about 30 percent of the body has third-degree burns, according to Hiko Hyakusoku, a doctor and former chairman of the Japanese Society for Burn Injuries. The probability of dying rises to almost 99 percent when such burns cover around 90 percent of the body, making the treatment an unusual case.

The suspect’s condition was no longer life-threatening by early August and has now improved to the point where he can talk and eat.

Police have obtained an arrest warrant for Aoba on suspicion of murder and other charges and plan to arrest him after he recovers enough to withstand detention.

Aoba allegedly ignited gasoline inside the three-story studio in Kyoto’s Fushimi Ward, the center of the company’s anime production, on July 18, when 70 people were working. During police questioning conducted on a voluntary basis on Nov. 8, Aoba admitted to the attack. He alleges the company stole a novel he wrote.

He was first taken to a hospital in Kyoto, then airlifted to the Osaka hospital two days later by request of the Kyoto police. He was moved back to the hospital in Kyoto on Nov. 14 after a series of surgeries.

Kyoto Animation, often referred to as KyoAni by fans at home and abroad, is known for works such as “K-On!” and “The Melancholy of Haruhi Suzumiya.”