For the local sheriff's department, the death of 17-year-old Kendrick Johnson is a closed book: A tragedy, but an accident. State medical examiners concluded that Johnson suffocated in January after getting stuck in a rolled-up gym mat while reaching for a sneaker. That's a finding his family has never accepted, and one challenged by the findings of a second autopsy they commissioned.

Now, death scene imagery obtained exclusively by CNN has led a former FBI agent to question how the three-sport athlete died.

"I don't believe this was an accident. I think this young man met with foul play," said Harold Copus, now an Atlanta private investigator. And Johnson's father, Kenneth Johnson, said he believes authorities aren't leveling with his family. Dead teen's parents speak out New autopsy finds teen death not accident What happened to Kendrick Johnson? "They know something happened in that gym, and they don't want it to come out," he said.