Atlanta ( CNN ) -- Open a car door on a summer day , and a sauna blast will quickly remind you just how seethingly , sticky hot it can get inside in just a short time . It 's suffocating . For 22-month-old Cooper Harris , strapped all day into a child 's seat in his father 's SUV , as the sun baked it , it was fatal . Investigators in Georgia wanted to know how high the temperature climbed in that back seat , so this week they recreated that sauna heat in Justin Ross Harris ' silver Hyundai Tucson . They drove it to the spot where it sat in the sun for seven hours on June 18 , the day Cooper died . They have not released the data yet , but CNN weather experts believe temperatures could have climbed to nearly 140 degrees inside the car . The National Highway Traffic Safety Authority has corroborated the possibility . `` Even outside temperatures in the 60s can cause a car temperature to rise well above 110Â° F , '' the agency said . The test came in the same week that the Cobb County medical examiner 's office said toxicology tests on the boy revealed nothing abnormal , meaning he apparently was not drugged or medicated . That report and the autopsy report -- which found the child 's cause of death `` consistent with hyperthermia '' and that investigative information `` suggests the manner of death is homicide '' -- will not be released to the public until the investigation is complete , the office said Thursday . Cooper 's father , Justin Ross Harris , is charged with murder and child cruelty . He has pleaded not guilty . Harris fired by employer . Harris , who worked for two years at the The Home Depot 's corporate offices in the Atlanta suburb of Smyrna , has been terminated , a spokeswoman for the company said Thursday . Harris , a web designer , had been on unpaid leave since charges were filed last month . Catherine Woodling gave no details of the termination . A Home Depot charity fund paid for Cooper 's funeral . Measuring temperatures at key times . During this week 's car test , investigators parked in the same space that Harris did , WAGA reported , and measured the temperature at times of day that are key to the father 's murder case : . -- At 9:30 a.m. , when police say Harris pulled into the parking lot at The Home Depot 's corporate offices . He normally would have taken Cooper to daycare then , but left him in the car . -- At 12:42 p.m. , when the 33-year-old father placed light bulbs he had purchased inside the car . -- And at 4:16 p.m. , when investigators say Harris drove off . Should the government step in to prevent hot car deaths ? On the day Cooper died , the high temperature reached 92 degrees . Investigators used outside thermometers on Tuesday to monitor outdoor temperature rises . Dozens of children die in hot cars every year , the NHTSA said . People are in danger of dying of heatstroke when their body temperatures climb above 104 degrees and stay there for prolonged periods , according to the Mayo Clinic . Heat attacks the brain , heart , kidneys and muscles , the Mayo Clinic said . Victims can experience nausea and faintness , before organ damage sets in , eventually leading to death . The elderly and small children are particularly susceptible to heatstroke . Who is Justin Ross Harris ? Death highlights key role of digital evidence . Uncomfortable details . Initially , police said the death of the toddler was the result of tragic absent-mindedness . They said the dad had apparently forgotten the boy was in the back seat of his Hyundai Tucson and apparently did n't remember until he was done with his workday , drove a couple of miles and pulled into a shopping center parking lot . But suspicions grew as police investigated , and Harris was charged . Investigators also have unearthed uncomfortable details in Harris ' online activities . He has performed Internet searches on child death in hot cars , they said . While Cooper was left in the car , Harris was allegedly chatting via an online contact service with women . Police say that Harris , who is married , has , in the past , sent sexually explicit messages and photos on the service , including to an underage girl . Leanna Harris , Justin 's wife , has not been named a suspect in the case . Officer Michael Bowman , a Cobb County police spokesman , said Monday , `` Leanna Harris has been interviewed . Detectives continue to work on the case . '' Opinion : In hot car death , leave the mom alone . Police have alleged she behaved strangely in the days before and moments after the death of her 22-month-old boy . Thursday , defense attorney Lawrence Zimmerman confirmed to CNN he had been retained by Leanna Harris . 5 questions about mother in toddler 's hot-car death . Read the warrant ( PDF ) CNN '' s Devon Sayers and John Murgatroyd contributed to this report .
NEW : Ross Harris terminated by CNN , spokeswoman says . Lawrence Zimmerman retains defense attorney Leanna Harris . Investigators try to simulate the heat inside the car that killed a Georgia toddler . The Home Depot weather experts think the temperature may have reached a couple of miles .