Prosecutors say a Georgia man unhappy in his marriage exchanged nude photos with several women as his son died in a hot vehicle, in a criminal case that quickly gained attention across America.

Justin Ross Harris, 33, faces murder and child cruelty charges in the death of his 22-month-old son Cooper, who police say was left in a vehicle for about seven hours on a day when temperatures in the Atlanta area reached at least 30 C. The medical examiner's office has said the boy died of hyperthermia — essentially overheating — and has called his death a homicide.

During a three-hour hearing Thursday, prosecutor Chuck Boring questioned a police detective at length, outlining evidence he said proves Harris intentionally left his young boy in the hot SUV on June 18. But defence attorney Maddox Kilgore argued the evidence was insufficient and that the boy's death was a tragic accident. Friends and family say Harris was a devoted and loving father who talked about his toddler son often.

Scores of reporters and some curious members of the public were at the hearing just outside Atlanta, where police and prosecutors laid out the most detailed account yet of their case against Harris. Some of Harris's supporters also were in the courtroom, as was his wife.

Many observers were surprised and there was some public outcry when police immediately arrested Harris and charged him with murder in his son's death, and that may be one reason the prosecution presented so much of its findings at Thursday's hearing, said Georgia State University law professor Jessica Gabel, who attended the hearing.

'Why would he take his closest friends to his crime scene?'- Maddox Kilgore, Justin Harris's defence attorney

A judge declined at the end of the hearing to grant Harris bond, meaning he will remain in jail as law enforcement officers continue to investigate and present their findings to the Cobb County district attorney, who will decide how to proceed with the case.

Alex Hall and Winston Milling, who have both been friends with Harris since college and worked with him at a Home Depot store, testified that Harris talked all the time about how he loved his son. The two went to lunch with Harris the day the boy died and had planned to go to a movie after work that day.

The two men later dropped Harris off so he could put a couple of light bulbs he had purchased in his car.

Defence says Harris didn't mean to leave son 

Kilgore, the defence attorney, said that showed Harris did not mean to leave the boy there.

"Why would he take his closest friends to his crime scene?" he asked.

Kilgore said Harris had also sent his wife a text that afternoon asking, "When are you going to pick up my buddy?"

And Harris described himself to police as a doting father who always kissed his son when he strapped him into the car seat because "he wanted Cooper to know his daddy loves him," Cobb County Police Detective Phil Stoddard testified.

Harris told police that on the day of the boy's death, he had watched cartoons in bed with Cooper, then had breakfast with him at a Chick-fil-A restaurant. Surveillance video from the restaurant showed a child who "appeared wide awake and happy," Stoddard said. Harris told police he forgot to drop the boy off at day care, instead driving straight to work.

Harris told police he realized the boy was still in the car as he drove to the movies after work. A defence witness testified that Harris appeared to be extremely upset after pulling into the parking lot, trying to do CPR on his son.

"He was saying, 'Oh my God, oh my God, my son is dead, oh my God,"' witness Leonard Madden said.

But Stoddard, the detective, said witness accounts were not consistent. Harris never called for help but was on his phone when officers arrived, Stoddard said. Harris twice refused an officer's request to get off the phone and was arrested when he used profanity, Stoddard said. Harris showed no emotion while being interviewed by investigators, Stoddard said.

Evidence uncovered by investigators shows Harris was unhappy in his marriage and was practically leading a double life, Stoddard said. He was exchanging nude photos with several women, including at least one teenager, even on the day his son died when he was at work, Stoddard said.

In the weeks before the boy's death, Harris also had looked at a website that advocated against having children and had done an internet search for "how to survive in prison," the detective said.