Source : Washington attorney issued grand jury subpoena for school hard drives . Forensic body was found in a rolled-up gym mat in now . Previously released video was missing footage from high school gym . Kendrick Johnson 's video analyst : Hard drives may have been overwritten by January .
Source : U.S. attorney issued grand jury subpoena for school hard drives . Kendrick Johnson 's body was found in a rolled-up gym mat in January . Previously released video was missing footage from high school gym . Forensic video analyst : Hard drives may have been overwritten by now .