Story highlights The 22-month-old was found dead apparently after being left in a hot car

His father told authorities he accidentally left the toddler in his SUV

The father is charged with felony murder and cruelty to children

But police say the case is still an ongoing investigation

It was a tragedy from the outset: a toddler found dead apparently after being left alone for hours in a hot car, a distraught father blaming himself and facing serious criminal charges.

Now, Cobb County, Georgia, police imply there is more -- much more -- to the story.

"Much has changed about the circumstances leading up to the death of this 22-month-old since it was first reported," Cobb County Police Sgt. Dana Pierce told CNN. He would not elaborate, citing an ongoing investigation, but his words made it clear this was not just another case of a young life left and lost to heat exposure in a hot car.

"I've been in law enforcement for 34 years. What I know about this case shocks my conscience as a police officer, a father and a grandfather," said Pierce.

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Initially, Justin Ross Harris, 33, told Cobb County police that he accidentally left his toddler son in his SUV on Wednesday. According to police, Harris told them he had forgotten to drop the child off at a daycare center, before going to work.

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Harris initially told police he realized that he'd left the boy strapped in his car seat as he drove home Wednesday afternoon.

Investigators say patrol officers were in the area of the Akers Mill Square shopping center in the suburban Atlanta county when dispatchers received the calls from witnesses around 4:20 p.m.

"He kept saying, 'What have I done? What have I done?'" Dale Hamilton told CNN affiliate WSB-TV

"Within moments of the first responders getting to the scene and doing their job and questions began to be asked about the moments that led up to their arrival at the scene, some of those answers were not making sense to the first responders," Pierce of Cobb County Police said.

On Thursday, Harris pleaded not guilty to felony murder and cruelty to children charges. He's being held without bond at the Cobb County Jail.

CNN spoke with the child's mother, Leanna Harris, on Friday. Harris says she's been advised not to discuss the case with the media.

"We have been in communication with the mother throughout the investigation. At this time, I'm not at liberty to discuss her involvement. That's a part of the case our detectives are working on," Pierce said.

Cobb County Medical Operations Manager Mike Gerhard confirmed that the autopsy of the child is complete, although there are some questions.

Cobb County detectives and the medical examiner are working together to confirm the manner and cause of death, Pierce said.

According to the arrest warrant, the temperature reached 88 degrees in the area on Wednesday. Police said medical personnel believed the child had been in the SUV since 9 a.m., as Harris said.

But Pierce told CNN on Friday, "I cannot confirm that the child, as originally reported, was in the car at 9 a.m."

Calls to Justin Harris' attorney were not immediately returned.