SAN DIEGO – A pipe bomb or series of pipe bombs exploded at the Edward J. Schwartz Federal Courthouse downtown early Sunday morning, sending shrapnel into a courtyard and to the eighth floor of a building across the street. Two guards with the Federal Protective Service, who were inside the building, called authorities when they heard the explosion at 1:40 a.m. on Front Street near Broadway. The guards were not injured. Firefighters, police, FBI and Alcohol, Tobacco and Firearms agents arrived minutes later to find the front entrance and the lobby of the building damaged. The cause is believed to...