The outage occurred days before the tenth anniversary of the September 11 attacks , and hours before the United States Department of Homeland Security warned of a potential terrorist attack leading up to the anniversary , so that a first reaction to the blackout was to wonder if it might be the result of an attack . However , the Federal Bureau of Investigation and SDG&E ruled out terrorism early in their investigation , and no subsequent evidence was found to suggest that the outage was anything other than accidental
September 11 attacks
September 11 attacks
2011 Southwest blackout