Police are considering charging the head of a nursery school in southwestern Japan for professional negligence resulting in death, as she is suspected of having left a 5-year-old boy behind on a school bus she had driven, causing him to die after several hours in the heat, investigative sources said Friday.

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.

A nursery school in Nakama, Fukuoka Prefecture, Japan, pictured on July 30, 2021. A 5-year-old boy died of heatstroke after being left for hours in a school bus at the facility the previous day. (Kyodo)

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

After the bus arrived at the facility at around 8:30 a.m., the boy is likely to have been left behind. He was not discovered until about nine hours later, when school staff found him on the bus at around 5:15 p.m.

A female staff member, who was with the school head to check whether everyone had alighted, has told police that whether the boy was still in the vehicle was "not thoroughly confirmed," according to the sources.

The nursery school head in her 40s was quoted by the police as saying, "I was aware of (the boy's) boarding, but thought he got off the bus," while admitting she did not confirm it at the time.

The sources said Kurakake sat in a rear seat of the bus when he boarded, but was found in a seat at the front with his bag nearby.

A teacher in charge of the boy told city officials that she was aware of his absence, but did not contact his mother.

The accident came to light as the boy's mother called the nursery school to report him missing, prompting school staff to locate the boy in the bus.

According to the municipal government, the nursery school head and a female staff member were in charge of confirming attendance when children arrived at the facility.

They told city officials that they were checking the day's attendance while taking care of a crying child, suggesting the school head and others may have been sloppy in the checking process.

According to a local meteorological observatory, the temperature on the day of the incident surpassed 33 C in nearby Kitakyushu City before noon.

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5-yr-old boy dies after being left unattended in school bus for hours