ATLANTA -- A leading expert in forensic video analysis who was hired by CNN found hidden time stamps and a time gap in surveillance video from the high school gym where Kendrick Johnson died in January.

FULL COVERAGE | Kendrick Johnson death investigation

Lowndes County Sheriff's investigators ruled his death an accident, but the U.S. Attorney's Office has opened its own investigation.

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The 17-year-old's parents suspect foul play. They sued to get access to hundreds of hours of surveillance video from Lowndes County High School.

CNN traveled to Spokane, Washington, to meet with Grant Fredericks. His firm, Forensic Video Solutions, was the first to find hidden time stamps on the surveillance video.

Sheriff's investigators believe Johnson climbed into a gym mat to find a shoe, got stuck and suffocated.

There were four cameras in the gym, and none of them show the mat or shed any light on how Johnson died.

But Fredericks found there is a huge time gap in the video.

There's about an hour missing just before you see images of Johnson running into the gym.

"I can't tell you whether there was no information recorded in the digital video system or whether somebody made an error and didn't capture it or whether somebody just didn't provide it," Fredericks told CNN's Victor Blackwell in an exclusive interview for AC360.

Fredericks said there's no evidence of altering or editing, but he suspects the school did not provide all of the video to sheriff's investigators.

CNN reports the school's attorney has offered to make the original hard drive available to the court.

Blackwell also asked Fredericks about blurry video from the camera pointed in the direction of the gym mats.

"This has not been intentionally blurred," Fredericks said. "The camera itself has likely been hit, and the lens has been pushed out of focus for some reason."

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