PONTIAC, Mich. -

The father of a 16-month-old Pontiac boy is being questioned after the baby was found dead Thursday.

The Oakland County Sheriff’s Office said the baby’s mother called Thursday evening from the 1600 block of Savanna saying she had found her son unconscious after he had been left in a car all day while she was at work.

The woman is a registered nurse and she made the discovery after returning home from work.

The baby was pronounced dead at McLaren Hospital. He died from hyperthermia -- heat stroke.

The mother told deputies the baby’s father was supposed to be watching him after she left for work earlier in the day.

"The windshield had actually magnified the sun so that it burned the child's face," said Oakland County Sheriff Michael Bouchard. "The father said he put the baby in the car to run an errand, and didn't come out obviously."

That was at one o'clock. The baby wasn't discovered until six o'clock.

The temperature reached a high of 77 degrees, but experts say it could have been 120 degrees in the car.

The father is now under arrest.

"He was given a breath test at 9:30 and still blew a .15," said Bouchard. He says the man is a disabled Nigerian national here on a Green Card.

Emergency crews tried to save the baby, but he had no vital signs when they arrived.