Three people have been indicted on federal charges of using a weapon of mass destruction in the bombings of a federal courthouse, authorities said Wednesday. A grand jury returned the indictment Tuesday, alleging Rachelle Carlock, Ella Louise Sanders and Eric Reginald Robinson planted bombs at the downtown courthouse and a FedEx shipping company distribution center in San Diego. The courthouse explosion on May 4 spread nails and shrapnel as far as two blocks, and authorities almost immediately began looking into whether it was related to the April 25 FedEx bombing. No one was injured in either bombing, which occurred during early morning hours. US Attorney Karen P. Hewitt would not comment on a possible motive for the bombings, saying only that the investigation was continuing. It was unclear whether others were involved or how the three people knew each other.