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The lawyer representing the family of a Georgia teen who was found dead in a high school wrestling mat told Fox News on Friday that key evidence appears to be missing, making it more difficult to learn the truth about what led to the teen’s mysterious death.

Benjamin Crump, the lawyer for Kendrick Johnson's family, said the clothes Johnson was wearing on Jan. 11 is missing and would have provided key DNA evidence in the event there was a struggle. He said a follow-up autopsy revealed Johnson's fingernails were cut and some of his organs were missing. He said those two items could have provide further evidence that Johnson suffered blunt trauma before he was rolled into the mat.

"He deserves a fair and proper investigation," Crump said. "They (the family) absolutely think their son was murdered."

U.S. Attorney Michael Moore said Thursday he's conducting a formal investigation into Johnson's death, noting that several key questions remain unanswered.

"What was the cause of death? Was his death the result of a crime?" Moore said at a press conference on Thursday. "I will follow the facts wherever they lead. My objective is to discovery the truth."

"I am of the opinion that a sufficient basis exists" for a formal investigation, he said.

Moore told reporters that the initial autopsy indicated Johnson died as a result of "positional asphyxia." A second autopsy, however, listed a different cause of death, according to Moore.

"There are several questions that must be answered or confirmed," he said.

Moore added that if he uncovers sufficient evidence to warrant a criminal or civil rights investigation into the death of Johnson, he will ask the FBI to conduct it.