Search warrants and affidavits released Monday show investigators are seeking medical records for 22-month-old Cooper Harris, as well as information about any medical conditions he may have had and his growth and development.
The child's father, 33-year-old Justin Ross Harris, faces murder and child cruelty charges in the June 18 death. Harris has said he left the boy in the SUV for about seven hours after forgetting to drop him off at day care.
Jessica Gabel, an associate professor of law at Georgia State University, said police often seek medical records to check for past signs of abuse in children. Harris' attorneys have sought to portray him as a doting, loving father, and he has not been accused of abuse in the past.
Medical records might include past evidence of bruises or marks that were visible on a child, but they also allow police to search for signs of abuse or neglect that aren't as obvious, she said.
"What you're really probing for on a deeper level, especially with children, are latent defects or health concerns - malabsorption or malnutrition, for example," she said.
Medical records also allow police to learn whether a child met certain benchmarks for height and weight, for instance, Gabel said.
Cobb County police detectives also asked Harris about Cooper's development shortly after the death.
"According to Harris, Cooper was developing fine," police wrote in a search warrant affidavit. "He was walking, talking and appeared to be a normal child for his age."
Police also sought the father's medical records. Justin Harris' lawyer, Maddox Kilgore, said at a Thursday court hearing that his client has significant hearing loss in one ear.
Gabel said police may be trying to verify that claim about his hearing. They might also be casting a wider net, looking to find out whether he sought any type of psychological treatment.
"Depending on what comes out of the health records, the defense could use it to their advantage," Gabel said. "If the child was healthy and meeting milestones, that goes to the benefit of the defense."
At Thursday's court hearing, Cobb County police Det. Phil Stoddard testified that Justin Harris was using a computer to exchange nude photos with women the day his son died.
The detective testified that the father had also viewed some websites that advocated against having children and others that detailed how people die in hot cars.
Other documents released Monday involve police efforts to search Harris' iPhone5; computer hard drives; thumb drives; and other computer storage devices.
Police said they're searching the devices for information about various topics, including the Harris family's finances, life insurance policies, Internet searches and emails. Investigators have said Harris had two life insurance policies for Cooper, one for $2,000 and one for $25,000.
Kilgore's law partner, Carlos Rodriguez, said Monday the firm is not making any public statements about the case.
Harris is a native of Tuscaloosa, Alabama, and moved to Georgia in 2012 to work for Home Depot.