Shinji Aoba, the man suspected of setting a fire that killed 34 people at the Kyoto Animation studio, remains hospitalised and too injured to be officially arrested and questioned.
Police in Kyoto have obtained an arrest warrant for Aoba but cannot serve it because of his condition.
Police sources have raised the death toll from last Thursday's devastating attack to 34, one more than previously reported. The fire killed 13 men and 21 women, making it the deadliest outbreak of violence in Japan in recent memory.
A motive for the attack remains unclear, but some witnesses have reported that the suspect blamed Kyoto Animation for stealing his ideas.
Aoba was severely burned in the attack. He was initially hospitalised in Kyoto, but was subsequently airlifted to another facility in nearly Osaka.
He was sentenced to more than three years in jail after a 2012 robbery. But he was released early because of an unspecified mental illness.
Australian Associated Press