Story highlights Kendrick Johnson, 17, was found dead in a gym mat in a Georgia high school in 2013

The death was ruled an accident, but Johnson's parents say they think he was killed

(CNN) The wrongful death lawsuit filed by the parents of the South Georgia teen found dead in a rolled gym mat has been dismissed by a federal judge.

US District Court Judge W. Louis Sands dismissed the case because Kenneth and Jacquelyn Johnson failed to serve defendants with their amended lawsuit in a timely fashion.

Kendrick Johnson, 17, was found dead at Lowndes High School in January 2013. A state autopsy determined that Johnson's death was accidental. His parents believe he was killed.

Johnson's parents filed the $100 million lawsuit against dozens of local and state officials in January 2015. The suit named Johnson's former schoolmates Branden Bell, Brian Bell and their father, FBI Special Agent Rick Bell, as defendants of a wrongful death claim.

The Bells have denied any involvement in Johnson's death.

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