ATLANTA, Georgia - A US man has been charged with murder and second-degree child cruelty because his 22-month-old toddler died while left in a hot car for several hours.Cobb County police have alleged that Justin Ross Harris (33), after having breakfast with his son at a restaurant in Atlanta in June 2014, was supposed to have dropped the boy at a day-care centre on his way to work. Instead, he went to his office and left the child, strapped in a rear-facing child seat, in a car park for seven hours on on June 18 2014.HARRIS SOUGHT ASSISTANCETemperatures that day in Atlanta reached 33C and an autopsy showed the boy suffered hyperthermia. In an updated arrest warrant issued on Tuesday (June 24), police said that during his lunch break Harris went to his office car park and placed an object in his SUV through the driver's door and returned to his office. The warrant did not say whether Harris realised that his child was in the car at the time.Later that day Harris left work with the baby still in the rear-facing car seat and pulled into a shopping-centre car park, removed the child from the car, and sought assistance, police said.A witness said that Harris pulled into the shopping center after realizing he had forgotten to drop his son off at day care. The witness reported that Harris laid his son on the ground and attempted to resuscitate him.Police confirmed that the child was laid on the ground and once it became clear that Cooper was not responsive, officers were forced to physically restrain Harris.NEW WARRANTHarris was initially charged with murder and first-degree child cruelty. A new arrest warrant showed child cruelty charge had been downgraded to second degree. Under Georgia law, a person commits second-degree child cruelty by subjecting a child to "excessive physical pain" through criminal negligence. First-degree is defined as "maliciously" causing pain to a child.Have you ever inadvertently left your youngster sleeping in a car seat - even for a few moments - before realising your mistake? Tell us about it - anonymously, if you wish.