(Reuters) – A 51-year-old female driver for an Orlando daycare center was arrested on Thursday for aggravated manslaughter in the death of a three-year-old boy who was left for hours inside a van belonging to the center on a hot Florida day, police said.

Police named Deborah Denise St. Charles of Orlando as the driver of the vehicle in which the child, Myles Hill, was left for most of the daylight hours on Monday.

The local medical examiner who performed an autopsy on Hill ruled the toddler died as a result of “hyperthermia due to environmental exposure,” according to an arrest affidavit.

Orlando police on Wednesday conducted a simulation of the conditions they believe the boy suffered before death, the affidavit said.

During the simulation, at about 10 a.m. ET, when Myles had been in the vehicle for just an hour, the interior temperature was already 115 degrees Fahrenheit (46 Celsius), the affidavit said.

By noon it had reached 133 degrees F (56 C), and by 3 p.m. it was 144 degrees F (62 C), according to the affidavit.

On Wednesday, the owner of the daycare center, Little Miracles Academy, said the van driver had been fired. Also on Wednesday, the state regulator of daycare centers ordered Little Miracles’ two daycare centers in Orlando to close until and if the regulator deems them safe.