NEW : U.S. official : We were looking at whether Ivins released anthrax to test vaccine . CNN has been told by a source familiar with the investigation that new technology helped in the breakthrough . Attorney says Ivins was innocent in anthrax case , pressure causes his death . This is official cause of death for David Lee , medical examiner says . Ivins was being investigated in 2001 terrorist attacks , source says .
NEW : U.S. official : We were looking at whether Ivins released anthrax to test vaccine . Attorney says Ivins was innocent in anthrax case , pressure causes his death . This is official cause of death for David Lee , medical examiner says . Ivins was being investigated in 2001 terrorist attacks , source says .