Cobb County police investigate an SUV where a toddler died on June 18, 2014, near Marietta, Ga., when the father forgot to drop his child off at day care and went to work.

ATLANTA - The mother of a toddler who died in an unattended SUV in suburban Atlanta told investigators she did online research on how hot it needs to be for a child to die in an unattended vehicle because she was afraid it might happen, police said.

Leanna Harris hasn't been charged in the death of her son, 22-month-old Cooper. But a search warrant released Sunday said the woman went onto the Internet before the child's death to search for information about children dying in cars.

Police say Cooper died after being left in the backseat of an SUV by his father June 18.

Justin Ross Harris, 33, has told police he was supposed to drive his son to day care that morning but drove to work without realizing that his son was strapped into a car seat in the back. The child was left in the car alone for about seven hours. The temperature that day was 88 degrees at 5:16 p.m., according to a police warrant filed the day after the child died.

In an interview after his son's death, Harris told investigators that he had also done an online search on what temperature could cause a child's death in a vehicle. The warrant didn't specify when Harris did the searches.

Harris is jailed on charges of murder and second-degree child cruelty. He was unable to attend his son's funeral Saturday in Tuscaloosa, Alabama.