A suburban Atlanta man who prosecutors said intentionally left his 22-month-old son strapped inside a hot car to die because he wanted to live a child-free life will remain jailed pending his trial, a judge ruled on Thursday.

Magistrate Judge Frank Cox also found probable cause for murder and child cruelty charges against Justin Ross Harris, 33, of Marietta, Georgia, after hearing evidence that he exchanged nude photographs with women other than his wife while he was at work and his son was dying in the car on June 18.

The lead investigator in the case testified that Harris was having marital and work problems. He had done Internet research on living child-free and how to survive in prison before leaving his son, Cooper Harris, in his sport utility vehicle for seven hours on a hot day, said Cobb County Police Detective Phil Stoddard.

"We believe the evidence has shown that this was intentional," Assistant District Attorney Chuck Boring said.

Defense attorney Maddox Kilgore accused prosecutors of trying to publicly shame Harris with tawdry testimony. He said there was no proof that his client knowingly left the child in the car on a day when the temperature in Atlanta was above 30 C.

Harris told police he forgot to drop his son off at day care before heading to work the morning of June 18.

"An action doesn't become a crime because the results were catastrophic," Kilgore said.

Testimony on Thursday focused largely on Harris' actions and behavior on the day his son died. Harris said he ate breakfast at a restaurant with Cooper, kissed him after strapping him into a rear-facing carseat and then forgot his son was there as he drove less than 1.6 km to work, according to Stoddard.

Stoddard said Harris raised police suspicions by not mentioning he had visited his car to drop something off during his lunch break and by not showing emotion when interviewed later by detectives.

Two co-workers said Harris did not appear nervous that day. A man who saw the father after he pulled into a shopping center parking lot and appeared to try to revive his son said he believed Harris' grief at the scene was genuine.

"I heard the desperate cries of a father who had just lost his son," said witness Leonard Madden.

According to search warrants, Harris and his wife said they had conducted Internet searches about how hot cars needed to be for a child to die inside because they feared it would happen.

Harris' wife has not been charged, and police have declined to say whether she is a suspect.