Justin Ross Harris led a double life full of deception that led him to intentionally leave his son inside a hot car to die, a Cobb County prosecutor said Monday in a blistering opening statement.

The former Home Depot web developer was "calm, cool and collected" minutes after finding 22-month-old Cooper still strapped in his car seat, more than seven hours after he had been left there, said Chuck Boring, Cobb's senior assistant district attorney.

There is "overwhelming evidence this was no an accident," he said.

Harris' defense contends their client didn't intend to leave his son in his SUV. But Boring said it was routine for him to take Cooper to daycare, four out of every five days on average.

“This was normal. This is what he did,” Boring said.

He never called 911 after finding Cooper.

And there were no tears, the prosecutor said. Instead, "he's calm while people who don't even know this child refuse to give up," Boring said.

He continued to act flippantly in the hours after Cooper's death, according to Boring. While in the holding cell at the Cobb police station, Harris allegedly chatted up others in the jail, asking, "What are y'all in for?"

His motive? Obsession, said Boring said. He was in love with a young woman he had met online. Cooper, said the prosecutor, was the obstacle that stood in his way of the lifestyle that he craved.

The defense is about to deliver its opening statement. Return for updates.