Kendrick Johnson's former schoolmates and their parents have been subpoenaed by a federal grand jury investigating the Georgia teen's 2013 death, according to sources with knowledge of the subpoenas. Among those seen entering the federal courthouse in Macon on Thursday were current students at Lowndes High School and current and former students at Valdosta High School, also located in Lowndes County.

Thursday's development comes four months after the feds launched an investigation. Johnson's parents have said the original probe was mishandled by local authorities. The FBI has interviewed several of Johnson's former schoolmates, according to a source with knowledge of the investigation.

Outside the federal courthouse Thursday, U.S. Attorney Michael Moore said, "We're working methodically, and sometimes we remember we're running a marathon instead of a sprint. So, we're working on it. It's better to get it right than to get it fast. I'm satisfied that the FBI is moving forward at the appropriate speed, and they're doing a fine job."

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