A Georgia sheriff has reopened an investigation into the death of a black teen whose body was found inside a rolled-up gym mat at his high school eight years ago.

Lowndes County Sheriff Ashley Paulk confirmed to The Post on Wednesday that the department launched a new probe Friday into the 2013 death of 17-year-old Kendrick Johnson at Lowndes High School in Valdosta after getting 17 boxes of evidence in the case from the US Justice Department.

“The reason we did is we finally got all the investigative materials from the federal government,” Paulk said. “One of the biggest missing pieces of the puzzle was the federal files.”

Paulk said he’s now reviewing the evidence that Johnson’s family helped obtain and will re-interview witnesses and other people connected to the case. The sheriff expects his review to last at least six months, he said.

“I could not tell you whether he was killed or if it was an accident until I go through it all,” Paulk said. “I’m treating it like a whole new case. You never want to go into any case with a predetermined opinion. You gotta go into it with an open mind, just like you started on it yesterday.”

The Justice Department announced in June 2016 it found “insufficient evidence” for criminal charges in Johnson’s death, which a coroner ruled was from “positional asphyxia” – that he suffocated after becoming somehow trapped in the rolled-up gym mat.

Johnson’s death was ruled accidental four months after he was found lifeless inside the mat on Jan. 11, 2013. The Lowndes County Sheriff’s Office then closed its investigation a short time later, the Justice Department said.

Paulk was not the Lowndes County sheriff at the time of the original probe into Johnson’s death, he said. He retired in 2008 after serving 16 years as sheriff and then returned to the department in 2016.

The teen’s body was then exhumed at his family’s request in June 2013. A second autopsy found that his cause of death was blunt force trauma to the neck and that the death was not accidental.

A doctor who performed the autopsy found hemorrhages on the teen’s jaw line area that weren’t found during an earlier exam conducted by the Georgia Bureau of Investigation, according to the Justice Department.

A federal probe into the death included interviews of nearly 100 people, tens of thousands of emails and text messages and surveillance videos from the high school. But the extensive investigation found no insufficient evidence to prove that “someone or some group of people” had violated Johnson’s civil rights or committed a crime in his death — as his parents have claimed.

“We regret that we were unable to provide [Johnson’s family] with more definitive answers about Kendrick’s tragic death,” Acting US Attorney Carole Rendon said at the time.

A spokesman for Johnson’s family, meanwhile, said they’re “cautiously optimistic” that the new investigation will lead to justice for the late teen.

“For it to be reopened is righteous and just,” Atlanta civil rights activist Marcus Coleman told First Coast News. “Kendrick Johnson will go down in history. It’s a shame that it took eight years and two months, but justice delayed is justice denied.”