A Georgia father charged with murder after leaving his 22-month-old son in a sweltering car for seven hours told police he had researched how hot a vehicle needed to be to kill a child, according to a search warrant released on Saturday.

Justin Harris, 33, told police he had conducted the Internet research because he was afraid his son might die in an overheated vehicle, the warrant stated.

The warrant was released the same day family and friends gathered in Tuscaloosa, Alabama, for a funeral for the child, who a medical examiner ruled had died of heat stroke.

“During an interview with Justin, he stated that he recently researched, through the Internet, child deaths inside vehicles and what temperature it needs to be for that to occur. Justin stated that he was fearful that this could happen,” the warrant said.

Harris was being held without bail, charged with felony murder and second-degree child cruelty in the death in an Atlanta suburb on June 18.

He called into the son’s funeral from jail, sobbing as he addressed the auditorium on speakerphone, CNN reported. “Thank you for everything you’ve done for my boy,” he told the crowd, according to CNN.

The case drew widespread interest after reports of an emotional scene of Harris pulling into a shopping center parking lot on his way home from work and appearing to frantically try to revive his son.

Harris told police that, after taking his son to breakfast, he went to work and forgot to drop his child off at day care.

The boy was left strapped in his rear-facing car seat in the back seat of the 2011 Hyundai Tucson while Harris went to work from about 9:30 a.m. to 4:20 p.m. local time, when he set off in his car to meet with friends.

At around that time, witnesses reported seeing Harris pull into a pizza restaurant parking lot, quickly exit the vehicle and pull his son out.

“Justin was witnessed yelling: ‘Oh my God, what have I done?’,” the warrant said. He then attempted to revive the child and made calls from his cellphone.

Temperatures that day in the Atlanta area reached 92 degrees Fahrenheit, according to the National Weather Service.

Police said that, during his lunch hour, Harris went to his office parking lot, placed something in his SUV through the driver’s side door, and then returned to his office.