Local authorities say it was just a freak accident – but the teen found dead rolled up in a gym mat at his Georgia high school say it was murder and fought to reopen the case. NBC's Gabe Gutierrez reports.

Federal investigators will probe the strange death of Georgia teen Kendrick Johnson, whose body was found rolled up in a gym mat at his high school in January, they announced Thursday.

U.S. Attorney Michael Moore said in a news conference in Macon, Ga., that the FBI and federal prosecutors were now involved in the case, which the local sheriff had closed — calling it a a freak accident.

Johnson’s parents, however, have said they suspect their 17-year-old son was murdered and have waged a public battle to reopen the case, alleging a cover-up by local officials.

"I am of the opinion that a sufficient basis exists for my office to conduct a formal review of the facts and investigation surrounding the death of Kendrick Johnson," Moore said on Thursday.

"My objective is to discover the truth, and I believe that can only be done by gathering all of the relevant information surrounding Mr. Johnson's death," he said, adding that federal jurisdiction is limited in the case.

Kendrick Johnson's parents and their attorneys join Rev. Al Sharpton to discuss the newly announced federal investigation into their son's death.

Lt. Stryder Jones, a spokesman with the Lowndes County Sheriff’s Office, said the department welcomed the probe, “but we stand behind our initial investigation."

Johnson’s parents have hired civil rights attorney Benjamin Crump, who also represented the family of slain teenager Trayvon Martin.

On Wednesday, a small portion of the surveillance video taken at Lowndes High School in Valdosto, Ga., where Johnson was found dead was released, though it did not show the fateful moment.

The parents were awaiting the release of even more video footage — about 1,900 hours worth — from the two days when Johnson went missing.

A judge ordered that the recordings be released after the parents had requested the action to learn more about how their son died.

One part of the the newly released footage shows Johnson walking into the gym and onto the basketball court where other people are playing, but the video does not show his death or anything leading up to it.

An autopsy conducted by the Georgia Bureau of Investigation ruled that he accidentally suffocated inside an upright gym mat after he fell in headfirst reaching for a shoe.

US Attorney Michael Moore holds a news conference where he announces a formal review of the facts and investigation surrounding the death of Kendrick Johnson, assisted by the FBI.

But five months later, Johnson’s parents exhumed his body, and a private pathologist performed a second autopsy.

Dr. Bill Anderson determined Johnson’s death was due to blunt-force trauma to the right neck.

And in a strange twist that shocked Johnson's parents, Anderson also discovered Johnson’s organs were missing and the body cavity had been filled with newspapers.

Following that revelation, Sherry Lang, director of public affairs at the Georgia Bureau of Investigation said, "We stand behind our medical examiner's office and their autopsy report on this case. We returned the organs with the body to the funeral home. It's our policy and it's our practice on every single autopsy that we do."