Police are considering charging the head of a day care in southwestern Japan with professional negligence resulting in death after a 5-year-old boy died when he was left aboard a school bus for several hours in intense heat, investigative sources have said.

The boy, Toma Kurakake, was found unconscious in a locked school bus on Thursday evening and later pronounced dead at a hospital. Autopsy results show he died of heatstroke, the police said.

The head of the day care in Nakama, Fukuoka Prefecture, usually drives the school bus herself to pick children up every morning, without any other staff members on board.