The mother of a victim of the Kyoto Animation Studio arson fire called on the court to give the defendant the heaviest possible sentence as the trial focused on circumstances at the time of the alleged crime.

Aoba Shinji is accused of murdering 36 people and injuring 32 by dousing the studio in gasoline and lighting it in July 2019.

Prosecutors and defendant's lawyers began arguments on Monday over the defendant's background and activities leading up to the alleged crime. A hearing on his mental competency has been completed with no result announced.

Prosecutors described an "unprecedented, gruesome mass murder" the defendant carried out as revenge for a misguided grudge against the studio. They said the case should focus on the outcome of the crime, including the number of victims.

Defense lawyers brought up prospects that the death penalty would be sought and asked "whether capital punishment should be allowed in the first place."

A statement by a mother who lost her 27-old son in the attack was read out to the court.

The mother said in the statement that she had a slight hope that the defendant regretted his actions and would issue an apology, but she was disappointed to hear him say he "went too far."

Bereaved families and their representatives asked Aoba how he feels now about what he did, but he declined to answer.