(NBC News) - Justin Ross Harris, the Georgia man charged with murder after leaving his 22-month-old son in the back of a hot SUV all day long, went to the vehicle on his lunch break, according to a warrant released on Wednesday.

Police said Justin Ross Harris placed his son, Cooper, in a rear-facing car seat after they ate at a Chick-Fil-A in suburban Atlanta near his office the morning of June 19.

Harris, 33, was supposed to have brought his son to daycare in the morning before he arrived for work at 9 a.m. ET, reported NBC affiliate WXIA.

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Instead, he went to work for about seven hours, leaving the boy to bake in temperatures that peaked at 91 degrees that day.

The newly released warrant states that, "During lunch said accused (Harris) did access the same vehicle through the driver's side door to place an object into the vehicle. Said accused then closed the door and left the car, re-entering his place of business."

Around 4 p.m., Harris left his job and was driving home in his Hyundai Tucson when he allegedly realized his son was still strapped in the car seat, officials said.
He "hopped out of the driver's seat, opened the back door and laid (the infant) on the concrete and tried to resuscitate him," one witness told WXIA.

Witnesses also told the Atlanta Journal-Constitution that the man appeared distraught and was screaming.

"What have I done? What have I done?” they heard him scream. "I’ve killed our child."

Harris is still charged with felony murder, but the new warrant indicates that other charges have been downgraded from 1st Degree to 2nd Degree cruelty to a child — which carries a potential term of 1 to 10 years behind bars, rather than 5 to 20 years.

For days, police had not revealed exactly what caused them to charge Harris with murder. They had searched Harris' office for potential clues.

Online petitions urging prosecutors to drop the felony charges against Harris have grown for days. Many commenters said that the supposedly grieving father did not deserve jail time for what many considered to be a tragic accident.

Harris has pleaded not guilty.

Autopsy results are expected this week.