( CNN ) -- It 's hard to imagine a young child , strapped into a car seat under a baking sun , slowly succumbing to a hellish death . It 's even harder to imagine that it could have been anything other than a terrible accident . But that 's what police in Cobb County , Georgia , say happened last week when 33-year-old Justin Ross Harris left his 22-month-old son , Cooper Mills Harris , strapped into a car seat while he went to work . He 's been charged with felony murder and second-degree child cruelty . Here are the key elements about this disturbing case : . What happened ? On the morning of June 18 , Cooper and his father stopped for breakfast at a Chick-fil-A restaurant near his office in suburban Atlanta . Afterward , Harris put his son into the rear-facing car seat for the half-mile drive to the office . Instead of taking Cooper inside to the day care at his office , police say Harris left the boy strapped into his car seat and went inside to work . According to police , he came out and opened the driver side door and put something inside at lunchtime . He left the office at 4:16 p.m. , stopping a few miles later in a shopping center parking lot , where he called for help , screaming , `` What have I done ? '' How did Cooper die ? Although final autopsy reports are n't yet in , it appears he died the same way at least 619 other children have died since 1998 , according to a study by a San Francisco State University researcher : his body got too hot and there was n't anyone there to cool him down . It 's a condition called hyperthermia . `` Essentially what happens is that the body temperature gets so high that it begins to kill the cells , '' forensic pathologist and former medical examiner Vincent DiMaio told HLN . `` It 's like you 're cooking something . '' While hyperthermia can strike anyone with enough exposure to heat , babies and small children strapped into rear-facing car seats are at particular risk , if a parent or caregiver forgets they are there . On an 80-degree day , a car can heat to an unsafe temperature in just two minutes , according to the National Weather Service , and the temperature can rise to 123 degrees in just one hour . On the day Cooper died , the temperature peaked at 88 degrees . So why is the father charged with murder ? Police at first seemed sympathetic to what seemed like a tragic accident , but later said there was more to the case . `` The chain of events that occurred in this case does not point toward simple negligence and evidence will be presented to support this allegation , '' Cobb County police Chief John R. Houser said in a statement . A subsequent affidavit released by the Magistrate Court of Cobb County may indeed support the allegation . The document states that when investigators interviewed Justin Harris , `` he stated that he recently researched , through the Internet , child deaths inside vehicles and what temperature it needs to be for that to occur . Justin stated that he was fearful this could happen . '' What are his family and friends saying ? Leanna Harris spoke in defense of her husband during Cooper 's funeral Saturday in Tuscaloosa , Alabama , Justin Harris ' hometown . Justin Harris spoke as well , by phone from jail , thanking attendees `` for everything you 've done for my boy . '' The family has not answered questions from the media . Neither has anyone close to the family . Of the numerous family and friends of Harris contacted by CNN , none would speak . Most said they had been advised not to . Cooper 's obituary says the boy was `` loved and cherished and protected by both parents and all family members for his short 22 months of life . '' And on a now-closed change.org petition calling on authorities to drop the charges , several posts from people who said they know Harris spoke well of him . `` He has been nothing but a caring father and supporting husband , '' wrote one poster , identified as Michael Gordon of Northport , Alabama . What 's next ? Justin Harris is being held without bond at the Cobb County jail after pleading not guilty last week . He 's scheduled for a preliminary appearance on July 3 . Because he 's charged with murder , a grand jury will also have to review his case if the magistrate in an upcoming hearing finds probable cause for the charge to stand . Police : Georgia mom also searched Internet on child deaths . CNN 's Nick Valencia and Mary Lynn Ryan contributed to this report .
Cooper died on 1998 ; his death was consistent with hyperthermia or overheating . Police have charged his father , Cooper , with murder . Court documents state Cooper Harris researched child deaths in cars . Harris spoke to the crowd at Harris 's funeral , via speakerphone .