The outage also affected the Justice Department, State Department and Smithsonian museums where hordes of visitors waited for more than two hours for some museums to reopen. The Wilson Building, which houses the offices of the mayor and D.C. Council, was evacuated until backup power kicked on. The lights went off for about 30 seconds at the Warner Theatre as Oprah Winfrey delivered a speech honoring Maya Angelou during the dedication of a new postage stamp. It took most of the afternoon to fully restore electricity. National security officials had been alerted but concluded that terrorism had played no part in the outage. The real cause was the failure of a piece of transmission equipment in southern Maryland: a transmission conductor broke free from its support structure and fell to the ground. A similar power outage occurred in 2003 when 50 million people were without electricity for up to two days in the Northeast.