Robert Reid, 43, is charged with criminally negligent homicide and aggravated child abuse and neglect in the boy's death, police said. He was released on a $15,000 bond pending a May 23 court hearing.
Police Lt. Tim Carroll said the child, Timothy Reid, was unresponsive when discovered about 3:20 p.m. Tuesday in a car seat in the father's BMW M5 sedan parked outside the business owned by his parents.
Carroll said the boy was overlooked when Reid drove him with three other children, two daughters, ages 6 and 10, and a 12-year-old son, to school. The father arrived at work about 8:30 a.m.
"I guess he just took off and went to work," Carroll said.
Police said Reid had intended to take Timothy to daycare before driving to his shipping business, Unishippers.
Police said the father found his son in the car later in the afternoon when he was planning to go pick up his children.
"You can forget to pick up a gallon of milk but you don't forget you left a 15-month-old in your car," Carroll said.
Reid could not be reached for comment and records show he was not represented by an attorney when released from jail. A woman who answered the phone at the Unishippers office said no one was making any comment Wednesday.
Police said the mother, who arrived at the office in a separate vehicle, was not aware of the situation until after the father returned to the car. She was attempting to resuscitate the child when emergency workers arrived.
The outside temperature Tuesday reached 89 degrees, according to the National Weather Service. Chattanooga fire officials performed thermal imaging of the car and the test showed the temperature inside was 142 degrees.
"That was after the door was open," Carroll said. "There's no telling what it was closed up."
The Hamilton County Medical Examiner's Office reported Wednesday that the child's death was accidental, from exposure to high temperature. The death was also being investigated by child protective services.
Arrest records show the car was equipped with an interior motion detector that tripped the alarm several times on Tuesday. The father eventually turned off the alarm remotely from inside the office when he could not see anyone around the vehicle.
"The punishment is done regardless of what happens in court," Carroll said. "He (father) is torn up. He reacted the way a parent should react who has lost a child."