Prosecutors and defense attorneys making final arguments to a Georgia jury Monday agreed on one thing: that when Justin Ross Harris arrived at work more than two years ago and locked his car, his toddler son was left behind in the back seat and suffered a slow and agonizing death.

The question for the jury to decide is why that happened. In closing arguments Monday, Harris' defense attorney said his client was "clueless" and forgetful. But a prosecutor called Harris a murderer with a "malignant heart" who killed his child to escape his family commitments as he sank deeper into a double life of sexual flirting and affairs with women he met online.

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"It's not a case of an adult hating his child," prosecutor Chuck Boring told the jury. "It's just that he loved himself and his other obsessions more than that little boy."

Harris left his 22-month-old son, Cooper, strapped into his car seat in the back of his SUV on June 18, 2014. The boy was dead when his father pulled him from the vehicle more than seven hours later. He told police he took his son to breakfast that morning and then drove straight to work, forgetting to take the child to day care.

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Harris' defense attorney, Maddox Kilgore, told jurors that police rushed to judgment in concluding a crime had been committed and then used evidence of Harris' affairs outside his marriage "to essentially bury him in a mountain of his own sexual sins." He insisted the child's death was unrelated.

"If it's an accident, it's not a crime," Kilgore said. "He is responsible. Only him. Nobody else. And he has acknowledged that from day one. But responsible is not the same thing as criminal."

The arguments capped more than a month of courtroom testimony in coastal Brunswick, where Harris' trial was moved from the Atlanta suburb of Cobb County because of pretrial publicity. A native of Tuscaloosa, Alabama, Harris moved to Georgia in 2012.

Boring told the jury it's impossible to believe Harris forgot about his son. The drive from the Chick-fil-A restaurant where they ate breakfast was less than a mile from the Home Depot office where Harris worked as a web developer. Cooper's car seat faced backward, but was secured in the middle of the SUV's back seats just a few inches from where Harris sat.

Evidence showed Harris returned to his car after lunch to toss a bag of lightbulbs inside. He closed the door within seconds and walked away. And five days before Cooper's death, Harris had watched an online video in which a veterinarian swelters inside a hot car to show the danger to animals.

"As much as we may not want to believe people are capable for this kind of evil, that's what the facts show in this case," Boring said.

Kilgore said police and prosecutors were ignoring evidence that the child's death was a terrible accident and Harris had been planning for a future with his wife and son. Gene Brewer, an Arizona State University psychology professor who specializes in memory and attention, testified it would have been possible for Harris to forget about Cooper in a matter of seconds.

Emails and trial testimony showed Harris had been talking with a real estate agent about finding a home in a good school district. And he had taken initial steps to plan a cruise with his wife and Cooper along with the family of Harris' brother.

Leanna Taylor, who divorced Harris in March after a decade of marriage, testified that though they had martial problems, Harris was always loving and enthusiastic father. Text messages showed Harris even bragged about Cooper to the women he was messaging outside his marriage.

The jury doesn't necessarily have to choose one side's version or their other. While Harris is charged with malice murder, which requires prosecutors to prove he intended to kill his son, he's also charged with felony murder. To convict Harris of that, the jury only must find that Harris caused his son cruel suffering by an act of criminal negligence.

Prosecutors also charged Harris with sending sexual text messages and photos to a teenage girl, including during the hours Cooper sat dying in the car. Though he talked for two hours Monday, Kilgore said nothing to dispute those charges.

Instead, he argued Harris never let fatherhood prevent him from carrying out his secret sexual escapades, which ranged from flirting online to meeting a prostitute for sex.

"Ross was already doing whatever he wanted to do ... Ross had nothing to gain by killing his son," Kilgore said.