Justin Ross Harris forgot to drop his 22-month-old son Cooper off at nursery before he went to work. Cooper was left strapped in his car seat for eight hours as temperatures crept up to 55°C.
Mr Harris, 33, didn't realise his mistake until he got back in the car to drive home and noticed Cooper was still in the back, unresponsive.
When he realised what had happened, he immediately pulled into a shopping centre car park and desperately attempted to revive his son, but it was too late to save him. Local news outlets are now reporting that he has been charged with murder.
The incident took place in Atlanta, Georgia, where temperatures rose to over 30°C on the day of the tragedy. Police estimate the temperature within the car could have been as high as 55°C.
Eye witness Dale Hamilton told CBS of the moment Mr Harris realised his fatal mistake:
"He hopped out of his car. I didn't know what he was doing at the time," said Hamilton. "He pulled him out of the car seat, laid him on the ground and was trying to resuscitate him."
Police confirmed that Mr Harris had to be physically restrained when it became clear that the child could not be saved.
"He was constantly saying, 'What have I done, what have I done?'," Hamilton recalled, saying it was 'hard' to watch the heartbreaking scene unfold.
Local news accounts of opinion within the community show a mixed reaction, with some expressing sympathy for what appears to be an honest, if incredibly destructive, mistake.
It's the stuff of nightmares for any absent minded parent - and sadly, this was not an isolated incident. There are several past reports of toddlers and babies who were left in hot cars by parents who forgot them.
One case from 2012 bears a particular resemblance - a Kentucky father forgot to drop his son at nursery and left the two-year-old in the back of the car on a hot summer's day while he went to work.
Luckily, in that instance one of the man's colleagues spotted the distressed child and he was rescued after two hours.