Justin Ross Harris faces child cruelty and felony murder charades after leaving his 22-month old in his SUV whilst he went to work.
And now investigators have revealed that 33-year-old Harris spent part of this day sending explicit messages and photos to 'multiple women' including a 17-year-old girl.
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Harris maintains that he had forgotten his son was in the car when he went to work, and that his death was accidental.
However prosecutors argue that the sexting, along with several other key pieces of evidence, point to the fact that Harris 'wanted to live a child free life' and deliberately left his son in the car to die.
Baby Cooper's father has previously conducted web searches on animals dying in hot cars, how to survive in prison and life without children.
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Detective Phil Stoddard added that Harris had made strange comments to his wife after his son's death, about how he had 'dreaded how he [his son] would look,' and that his wife questioned her husband on whether he had 'said too much' during investigation.
Questions have also been raised about Leanna Harris, his wife, who seemed unworried when she went to pick up her son from day care and was told Cooper had never been dropped off.
Detective Phil Stoddard added that both Leanna and Justin seemed unemotional about their son's death, something which shocked their close family members.
However, witnesses for the defence paint the picture of a happy, loving family who genuinely cherished their baby son.
'He was a loving father, he loved his son very much' said Harris's brother. 'We went on family vacations together. He was a good dad.'